diff --git a/src/common/cmake/Common.cmake b/src/common/cmake/Common.cmake
index 63c03441a94b..3dea1096123b 100644
--- a/src/common/cmake/Common.cmake
+++ b/src/common/cmake/Common.cmake
@@ -3,7 +3,7 @@
 include(ExternalProject)
 include(CMakeParseArguments)
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -g -Werror -Wall -Wno-error=unused-function -Wno-error=strict-aliasing")
 
 set(FLATBUFFERS_VERSION "1.7.1")
 
diff --git a/src/common/common.cc b/src/common/common.cc
index b8b1709b3670..c1f95a050a83 100644
--- a/src/common/common.cc
+++ b/src/common/common.cc
@@ -12,9 +12,6 @@
 #include "io.h"
 #include <functional>
 
-/* This is used to define the array of object IDs. */
-const UT_icd object_id_icd = {sizeof(ObjectID), NULL, NULL, NULL};
-
 const UniqueID NIL_ID = UniqueID::nil();
 
 const unsigned char NIL_DIGEST[DIGEST_SIZE] = {0};
diff --git a/src/common/common_protocol.cc b/src/common/common_protocol.cc
index 2787ce70f202..e746673fa10b 100644
--- a/src/common/common_protocol.cc
+++ b/src/common/common_protocol.cc
@@ -19,7 +19,7 @@ to_flatbuf(flatbuffers::FlatBufferBuilder &fbb,
            ObjectID object_ids[],
            int64_t num_objects) {
   std::vector<flatbuffers::Offset<flatbuffers::String>> results;
-  for (size_t i = 0; i < num_objects; i++) {
+  for (int64_t i = 0; i < num_objects; i++) {
     results.push_back(to_flatbuf(fbb, object_ids[i]));
   }
   return fbb.CreateVector(results);
diff --git a/src/common/io.cc b/src/common/io.cc
index 4ec28850cff4..4cf01e315a10 100644
--- a/src/common/io.cc
+++ b/src/common/io.cc
@@ -369,7 +369,7 @@ int64_t read_vector(int fd, int64_t *type, std::vector<uint8_t> &buffer) {
   if (closed) {
     goto disconnected;
   }
-  if (length > buffer.size()) {
+  if (static_cast<size_t>(length) > buffer.size()) {
     buffer.resize(length);
   }
   closed = read_bytes(fd, buffer.data(), length);
diff --git a/src/common/lib/python/common_extension.h b/src/common/lib/python/common_extension.h
index c91b631cd330..71830fc95d13 100644
--- a/src/common/lib/python/common_extension.h
+++ b/src/common/lib/python/common_extension.h
@@ -8,7 +8,7 @@
 #include "common.h"
 
 typedef uint8_t TaskSpec;
-struct TaskBuilder;
+class TaskBuilder;
 
 extern PyObject *CommonError;
 
diff --git a/src/common/state/error_table.cc b/src/common/state/error_table.cc
index 7453cd3c61b8..516bd98b85a3 100644
--- a/src/common/state/error_table.cc
+++ b/src/common/state/error_table.cc
@@ -1,6 +1,14 @@
 #include "error_table.h"
 #include "redis.h"
 
+const char *error_types[] = {"object_hash_mismatch", "put_reconstruction",
+                             "worker_died"};
+const char *error_messages[] = {
+    "A nondeterministic task was reexecuted.",
+    "An object created by ray.put was evicted and could not be reconstructed. "
+    "The driver may need to be restarted.",
+    "A worker died or was killed while executing a task."};
+
 void push_error(DBHandle *db_handle,
                 DBClientID driver_id,
                 int error_index,
diff --git a/src/common/state/error_table.h b/src/common/state/error_table.h
index f2f7c5651f07..0b297283fcf4 100644
--- a/src/common/state/error_table.h
+++ b/src/common/state/error_table.h
@@ -27,13 +27,8 @@ typedef enum {
 } error_index;
 
 /** Information about the error to be displayed to the user. */
-static const char *error_types[] = {"object_hash_mismatch",
-                                    "put_reconstruction", "worker_died"};
-static const char *error_messages[] = {
-    "A nondeterministic task was reexecuted.",
-    "An object created by ray.put was evicted and could not be reconstructed. "
-    "The driver may need to be restarted.",
-    "A worker died or was killed while executing a task."};
+extern const char *error_types[];
+extern const char *error_messages[];
 
 /**
  * Push an error to the given Python driver.
diff --git a/src/common/state/redis.cc b/src/common/state/redis.cc
index 58aca1ec53bb..bb7af45abcea 100644
--- a/src/common/state/redis.cc
+++ b/src/common/state/redis.cc
@@ -128,7 +128,7 @@ void get_redis_shards(redisContext *context,
     /* Try to read the Redis shard locations from the primary shard. If we find
      * that all of them are present, exit. */
     reply = (redisReply *) redisCommand(context, "LRANGE RedisShards 0 -1");
-    if (reply->elements == num_redis_shards) {
+    if (static_cast<int>(reply->elements) == num_redis_shards) {
       break;
     }
 
@@ -146,7 +146,7 @@ void get_redis_shards(redisContext *context,
   /* Parse the Redis shard addresses. */
   char db_shard_address[16];
   int db_shard_port;
-  for (int i = 0; i < reply->elements; ++i) {
+  for (size_t i = 0; i < reply->elements; ++i) {
     /* Parse the shard addresses and ports. */
     CHECK(reply->element[i]->type == REDIS_REPLY_STRING);
     CHECK(parse_ip_addr_port(reply->element[i]->str, db_shard_address,
@@ -297,7 +297,7 @@ DBHandle *db_connect(const std::string &db_primary_address,
   get_redis_shards(db->sync_context, db_shards_addresses, db_shards_ports);
   CHECKM(db_shards_addresses.size() > 0, "No Redis shards found");
   /* Connect to the shards. */
-  for (int i = 0; i < db_shards_addresses.size(); ++i) {
+  for (size_t i = 0; i < db_shards_addresses.size(); ++i) {
     db_connect_shard(db_shards_addresses[i], db_shards_ports[i], client,
                      client_type, node_ip_address, num_args, args, db, &context,
                      &subscribe_context, &sync_context);
@@ -317,7 +317,7 @@ void DBHandle_free(DBHandle *db) {
 
   /* Clean up the Redis shards. */
   CHECK(db->contexts.size() == db->subscribe_contexts.size());
-  for (int i = 0; i < db->contexts.size(); ++i) {
+  for (size_t i = 0; i < db->contexts.size(); ++i) {
     redisAsyncFree(db->contexts[i]);
     redisAsyncFree(db->subscribe_contexts[i]);
   }
@@ -360,7 +360,7 @@ void db_attach(DBHandle *db, event_loop *loop, bool reattach) {
   }
   /* Attach other redis shards to the event loop. */
   CHECK(db->contexts.size() == db->subscribe_contexts.size());
-  for (int i = 0; i < db->contexts.size(); ++i) {
+  for (size_t i = 0; i < db->contexts.size(); ++i) {
     int err = redisAeAttach(loop, db->contexts[i]);
     /* If the database is reattached in the tests, redis normally gives
      * an error which we can safely ignore. */
@@ -678,7 +678,7 @@ void redis_object_table_lookup_callback(redisAsyncContext *c,
     /* Extract the manager IDs from the response into a vector. */
     std::vector<DBClientID> manager_ids;
 
-    for (int j = 0; j < reply->elements; ++j) {
+    for (size_t j = 0; j < reply->elements; ++j) {
       CHECK(reply->element[j]->type == REDIS_REPLY_STRING);
       DBClientID manager_id;
       memcpy(manager_id.id, reply->element[j]->str, sizeof(manager_id.id));
@@ -777,7 +777,7 @@ void redis_object_table_subscribe_to_notifications(
    * src/common/redismodule/ray_redis_module.cc. */
   const char *object_channel_prefix = "OC:";
   const char *object_channel_bcast = "BCAST";
-  for (int i = 0; i < db->subscribe_contexts.size(); ++i) {
+  for (size_t i = 0; i < db->subscribe_contexts.size(); ++i) {
     int status = REDIS_OK;
     /* Subscribe to notifications from the object table. This uses the client ID
      * as the channel name so this channel is specific to this client.
@@ -1075,8 +1075,6 @@ void redis_task_table_subscribe_callback(redisAsyncContext *c,
       strcmp(message_type->str, "pmessage") == 0) {
     /* Handle a task table event. Parse the payload and call the callback. */
     auto message = flatbuffers::GetRoot<TaskReply>(payload->str);
-    /* Extract the task ID. */
-    TaskID task_id = from_flatbuf(message->task_id());
     /* Extract the scheduling state. */
     int64_t state = message->state();
     /* Extract the local scheduler ID. */
@@ -1188,7 +1186,7 @@ void redis_db_client_table_scan(DBHandle *db,
   }
   /* Get all the database client information. */
   CHECK(reply->type == REDIS_REPLY_ARRAY);
-  for (int i = 0; i < reply->elements; ++i) {
+  for (size_t i = 0; i < reply->elements; ++i) {
     redisReply *client_reply = (redisReply *) redisCommand(
         db->sync_context, "HGETALL %b", reply->element[i]->str,
         reply->element[i]->len);
@@ -1198,7 +1196,7 @@ void redis_db_client_table_scan(DBHandle *db,
     memset(&db_client, 0, sizeof(db_client));
     int num_fields = 0;
     /* Parse the fields into a DBClient. */
-    for (int j = 0; j < client_reply->elements; j = j + 2) {
+    for (size_t j = 0; j < client_reply->elements; j = j + 2) {
       const char *key = client_reply->element[j]->str;
       const char *value = client_reply->element[j + 1]->str;
       if (strcmp(key, "ray_client_id") == 0) {
diff --git a/src/common/task.cc b/src/common/task.cc
index c8d8f7d13c39..a78c16ac3715 100644
--- a/src/common/task.cc
+++ b/src/common/task.cc
@@ -72,10 +72,10 @@ class TaskBuilder {
   }
 
   void SetRequiredResource(int64_t resource_index, double value) {
-    if (resource_index >= resource_vector_.size()) {
+    if (static_cast<size_t>(resource_index) >= resource_vector_.size()) {
       /* Make sure the resource vector is constructed entry by entry,
        * in order. */
-      CHECK(resource_index == resource_vector_.size());
+      CHECK(static_cast<size_t>(resource_index) == resource_vector_.size());
       resource_vector_.resize(resource_index + 1);
     }
     resource_vector_[resource_index] = value;
diff --git a/src/common/task.h b/src/common/task.h
index db1b36899b84..ce2590a1e08d 100644
--- a/src/common/task.h
+++ b/src/common/task.h
@@ -10,7 +10,7 @@
 
 typedef uint8_t TaskSpec;
 
-struct TaskBuilder;
+class TaskBuilder;
 
 #define NIL_TASK_ID NIL_ID
 #define NIL_ACTOR_ID NIL_ID
diff --git a/src/common/test/task_table_tests.cc b/src/common/test/task_table_tests.cc
index 2fcb1d7aaa6a..2cae0e078850 100644
--- a/src/common/test/task_table_tests.cc
+++ b/src/common/test/task_table_tests.cc
@@ -161,7 +161,7 @@ TEST subscribe_timeout_test(void) {
                        (void *) subscribe_timeout_context);
   /* Disconnect the database to see if the subscribe times out. */
   close(db->subscribe_context->c.fd);
-  for (int i = 0; i < db->subscribe_contexts.size(); ++i) {
+  for (size_t i = 0; i < db->subscribe_contexts.size(); ++i) {
     close(db->subscribe_contexts[i]->c.fd);
   }
   aeProcessEvents(g_loop, AE_TIME_EVENTS);
@@ -176,7 +176,6 @@ TEST subscribe_timeout_test(void) {
 /* === Test publish timeout === */
 
 const char *publish_timeout_context = "publish_timeout";
-const int publish_test_number = 272;
 int publish_failed = 0;
 
 void publish_done_callback(TaskID task_id, void *user_context) {
@@ -205,7 +204,7 @@ TEST publish_timeout_test(void) {
                       (void *) publish_timeout_context);
   /* Disconnect the database to see if the publish times out. */
   close(db->context->c.fd);
-  for (int i = 0; i < db->contexts.size(); ++i) {
+  for (size_t i = 0; i < db->contexts.size(); ++i) {
     close(db->contexts[i]->c.fd);
   }
   aeProcessEvents(g_loop, AE_TIME_EVENTS);
@@ -227,7 +226,7 @@ int64_t reconnect_db_callback(event_loop *loop,
   redisAsyncFree(db->subscribe_context);
   db->subscribe_context = redisAsyncConnect("127.0.0.1", 6379);
   db->subscribe_context->data = (void *) db;
-  for (int i = 0; i < db->subscribe_contexts.size(); ++i) {
+  for (size_t i = 0; i < db->subscribe_contexts.size(); ++i) {
     redisAsyncFree(db->subscribe_contexts[i]);
     db->subscribe_contexts[i] = redisAsyncConnect("127.0.0.1", 6380 + i);
     db->subscribe_contexts[i]->data = (void *) db;
@@ -247,7 +246,6 @@ int64_t terminate_event_loop_callback(event_loop *loop,
 /* === Test subscribe retry === */
 
 const char *subscribe_retry_context = "subscribe_retry";
-const int subscribe_retry_test_number = 273;
 int subscribe_retry_succeeded = 0;
 
 void subscribe_retry_done_callback(ObjectID object_id, void *user_context) {
@@ -277,7 +275,7 @@ TEST subscribe_retry_test(void) {
                        (void *) subscribe_retry_context);
   /* Disconnect the database to see if the subscribe times out. */
   close(db->subscribe_context->c.fd);
-  for (int i = 0; i < db->subscribe_contexts.size(); ++i) {
+  for (size_t i = 0; i < db->subscribe_contexts.size(); ++i) {
     close(db->subscribe_contexts[i]->c.fd);
   }
   /* Install handler for reconnecting the database. */
@@ -329,7 +327,7 @@ TEST publish_retry_test(void) {
                       (void *) publish_retry_context);
   /* Disconnect the database to see if the publish times out. */
   close(db->subscribe_context->c.fd);
-  for (int i = 0; i < db->subscribe_contexts.size(); ++i) {
+  for (size_t i = 0; i < db->subscribe_contexts.size(); ++i) {
     close(db->subscribe_contexts[i]->c.fd);
   }
   /* Install handler for reconnecting the database. */
diff --git a/src/common/test/test_common.h b/src/common/test/test_common.h
index 94c6ef3bb1fc..9d482e91d459 100644
--- a/src/common/test/test_common.h
+++ b/src/common/test/test_common.h
@@ -60,7 +60,7 @@ static inline void flushall_redis(void) {
   /* Readd the shard locations. */
   freeReplyObject(redisCommand(context, "SET NumRedisShards %d",
                                db_shards_addresses.size()));
-  for (int i = 0; i < db_shards_addresses.size(); ++i) {
+  for (size_t i = 0; i < db_shards_addresses.size(); ++i) {
     freeReplyObject(redisCommand(context, "RPUSH RedisShards %s:%d",
                                  db_shards_addresses[i].c_str(),
                                  db_shards_ports[i]));
@@ -68,7 +68,7 @@ static inline void flushall_redis(void) {
   redisFree(context);
 
   /* Flush the remaining shards. */
-  for (int i = 0; i < db_shards_addresses.size(); ++i) {
+  for (size_t i = 0; i < db_shards_addresses.size(); ++i) {
     context = redisConnect(db_shards_addresses[i].c_str(), db_shards_ports[i]);
     freeReplyObject(redisCommand(context, "FLUSHALL"));
     redisFree(context);
diff --git a/src/global_scheduler/CMakeLists.txt b/src/global_scheduler/CMakeLists.txt
index 6e09b0c1cb55..bd6365bb8740 100644
--- a/src/global_scheduler/CMakeLists.txt
+++ b/src/global_scheduler/CMakeLists.txt
@@ -4,5 +4,7 @@ project(global_scheduler)
 
 include(${CMAKE_CURRENT_LIST_DIR}/../common/cmake/Common.cmake)
 
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror -Wall")
+
 add_executable(global_scheduler global_scheduler.cc global_scheduler_algorithm.cc)
 target_link_libraries(global_scheduler common ${HIREDIS_LIB})
diff --git a/src/global_scheduler/global_scheduler.cc b/src/global_scheduler/global_scheduler.cc
index 3650d85d3e95..2785caca956f 100644
--- a/src/global_scheduler/global_scheduler.cc
+++ b/src/global_scheduler/global_scheduler.cc
@@ -290,7 +290,7 @@ void object_table_subscribe_callback(
             ObjectID_to_string(object_id, id_string, ID_STRING_SIZE));
   ARROW_UNUSED(id_string);
   LOG_DEBUG("\tManagers<%d>:", manager_vector.size());
-  for (int i = 0; i < manager_vector.size(); i++) {
+  for (size_t i = 0; i < manager_vector.size(); i++) {
     LOG_DEBUG("\t\t%s", manager_vector[i]);
   }
 
@@ -304,7 +304,7 @@ void object_table_subscribe_callback(
     LOG_DEBUG("New object added to object_info_table with id = %s",
               ObjectID_to_string(object_id, id_string, ID_STRING_SIZE));
     LOG_DEBUG("\tmanager locations:");
-    for (int i = 0; i < manager_vector.size(); i++) {
+    for (size_t i = 0; i < manager_vector.size(); i++) {
       LOG_DEBUG("\t\t%s", manager_vector[i]);
     }
   }
@@ -314,7 +314,7 @@ void object_table_subscribe_callback(
 
   /* In all cases, replace the object location vector on each callback. */
   obj_info_entry.object_locations.clear();
-  for (int i = 0; i < manager_vector.size(); i++) {
+  for (size_t i = 0; i < manager_vector.size(); i++) {
     obj_info_entry.object_locations.push_back(std::string(manager_vector[i]));
   }
 }
diff --git a/src/global_scheduler/global_scheduler_algorithm.cc b/src/global_scheduler/global_scheduler_algorithm.cc
index 30c692f28773..79959d714da2 100644
--- a/src/global_scheduler/global_scheduler_algorithm.cc
+++ b/src/global_scheduler/global_scheduler_algorithm.cc
@@ -141,8 +141,7 @@ double calculate_cost_pending(const GlobalSchedulerState *state,
                               TaskSpec *task_spec) {
   /* Calculate how much data is already present on this machine. TODO(rkn): Note
    * that this information is not being used yet. Fix this. */
-  int64_t data_size =
-      locally_available_data_size(state, scheduler->id, task_spec);
+  locally_available_data_size(state, scheduler->id, task_spec);
   /* TODO(rkn): This logic does not load balance properly when the different
    * machines have different sizes. Fix this. */
   return scheduler->num_recent_tasks_sent + scheduler->info.task_queue_length;
@@ -157,11 +156,8 @@ bool handle_task_waiting(GlobalSchedulerState *state,
          "task wait handler encounted a task with NULL spec");
 
   bool task_feasible = false;
-  /* The total size of the task's data. */
-  int64_t task_object_size = 0;
 
   /* Go through all the nodes, calculate the score for each, pick max score. */
-  LocalScheduler *scheduler = NULL;
   double best_local_scheduler_score = INT32_MIN;
   CHECKM(best_local_scheduler_score < 0,
          "We might have a floating point underflow");
diff --git a/src/local_scheduler/CMakeLists.txt b/src/local_scheduler/CMakeLists.txt
index dbfe56d6f33d..c38a36ff2d41 100644
--- a/src/local_scheduler/CMakeLists.txt
+++ b/src/local_scheduler/CMakeLists.txt
@@ -19,7 +19,7 @@ endif(APPLE)
 
 include_directories("${PYTHON_INCLUDE_DIRS}")
 
-# set(CMAKE_C_FLAGS "${CMAKE_CXX_FLAGS} --std=c99 -Werror")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror -Wall")
 
 if(UNIX AND NOT APPLE)
   link_libraries(rt)
diff --git a/src/local_scheduler/local_scheduler_algorithm.cc b/src/local_scheduler/local_scheduler_algorithm.cc
index 9cfbc08c5b92..66343f134356 100644
--- a/src/local_scheduler/local_scheduler_algorithm.cc
+++ b/src/local_scheduler/local_scheduler_algorithm.cc
@@ -153,7 +153,7 @@ void SchedulingAlgorithmState_free(SchedulingAlgorithmState *algorithm_state) {
     remove_actor(algorithm_state, actor_id);
   }
   /* Free the list of cached actor task specs and the task specs themselves. */
-  for (int i = 0; i < algorithm_state->cached_submitted_actor_tasks.size();
+  for (size_t i = 0; i < algorithm_state->cached_submitted_actor_tasks.size();
        ++i) {
     TaskQueueEntry task = algorithm_state->cached_submitted_actor_tasks[i];
     TaskQueueEntry_free(&task);
@@ -682,7 +682,7 @@ int reconstruct_object_timeout_handler(event_loop *loop,
 
   int64_t max_num_to_reconstruct = 10000;
   int64_t num_reconstructed = 0;
-  for (int64_t i = 0; i < object_ids_to_reconstruct.size(); i++) {
+  for (size_t i = 0; i < object_ids_to_reconstruct.size(); i++) {
     ObjectID object_id = object_ids_to_reconstruct[i];
     /* Only call reconstruct if we are still missing the object. */
     if (state->algorithm_state->remote_objects.find(object_id) !=
@@ -1112,7 +1112,6 @@ void handle_actor_creation_notification(
 
   for (int i = 0; i < num_cached_actor_tasks; ++i) {
     TaskQueueEntry task = algorithm_state->cached_submitted_actor_tasks[i];
-    TaskSpec *spec = task.spec;
     /* Note that handle_actor_task_submitted may append the spec to the end of
      * the cached_submitted_actor_tasks array. */
     handle_actor_task_submitted(state, algorithm_state, task.spec,
diff --git a/src/local_scheduler/local_scheduler_client.cc b/src/local_scheduler/local_scheduler_client.cc
index 10886e7d2c53..ea34a5bfdcbb 100644
--- a/src/local_scheduler/local_scheduler_client.cc
+++ b/src/local_scheduler/local_scheduler_client.cc
@@ -45,7 +45,7 @@ LocalSchedulerConnection *LocalSchedulerConnection_init(
 
   /* Parse the reply object. */
   auto reply_message = flatbuffers::GetRoot<RegisterClientReply>(reply);
-  for (int i = 0; i < reply_message->gpu_ids()->size(); ++i) {
+  for (size_t i = 0; i < reply_message->gpu_ids()->size(); ++i) {
     result->gpu_ids.push_back(reply_message->gpu_ids()->Get(i));
   }
   /* If the worker is not an actor, there should not be any GPU IDs here. */
@@ -122,7 +122,7 @@ TaskSpec *local_scheduler_get_task(LocalSchedulerConnection *conn,
    * actor methods. */
   if (ActorID_equal(conn->actor_id, NIL_ACTOR_ID)) {
     conn->gpu_ids.clear();
-    for (int i = 0; i < reply_message->gpu_ids()->size(); ++i) {
+    for (size_t i = 0; i < reply_message->gpu_ids()->size(); ++i) {
       conn->gpu_ids.push_back(reply_message->gpu_ids()->Get(i));
     }
   }
diff --git a/src/local_scheduler/test/local_scheduler_tests.cc b/src/local_scheduler/test/local_scheduler_tests.cc
index 0bedbd3e53bc..bfa553eba467 100644
--- a/src/local_scheduler/test/local_scheduler_tests.cc
+++ b/src/local_scheduler/test/local_scheduler_tests.cc
@@ -610,7 +610,7 @@ TEST start_kill_workers_test(void) {
   /* We start off with num_workers children processes, but no workers
    * registered yet. */
   ASSERT_EQ(local_scheduler->local_scheduler_state->child_pids.size(),
-            num_workers);
+            static_cast<size_t>(num_workers));
   ASSERT_EQ(local_scheduler->local_scheduler_state->workers.size(), 0);
 
   /* Make sure that each worker connects to the local_scheduler scheduler. This
@@ -625,9 +625,9 @@ TEST start_kill_workers_test(void) {
    * workers accounted for, but we haven't yet matched up process IDs with our
    * children processes. */
   ASSERT_EQ(local_scheduler->local_scheduler_state->child_pids.size(),
-            num_workers);
+            static_cast<size_t>(num_workers));
   ASSERT_EQ(local_scheduler->local_scheduler_state->workers.size(),
-            num_workers);
+            static_cast<size_t>(num_workers));
 
   /* Each worker should register its process ID. */
   for (auto const &worker : local_scheduler->local_scheduler_state->workers) {
@@ -636,7 +636,7 @@ TEST start_kill_workers_test(void) {
   }
   ASSERT_EQ(local_scheduler->local_scheduler_state->child_pids.size(), 0);
   ASSERT_EQ(local_scheduler->local_scheduler_state->workers.size(),
-            num_workers);
+            static_cast<size_t>(num_workers));
 
   /* After killing a worker, its state is cleaned up. */
   LocalSchedulerClient *worker =
@@ -644,7 +644,7 @@ TEST start_kill_workers_test(void) {
   kill_worker(local_scheduler->local_scheduler_state, worker, false, false);
   ASSERT_EQ(local_scheduler->local_scheduler_state->child_pids.size(), 0);
   ASSERT_EQ(local_scheduler->local_scheduler_state->workers.size(),
-            num_workers - 1);
+            static_cast<size_t>(num_workers - 1));
 
   /* Start a worker after the local scheduler has been initialized. */
   start_worker(local_scheduler->local_scheduler_state, NIL_ACTOR_ID, false);
@@ -653,21 +653,21 @@ TEST start_kill_workers_test(void) {
   /* The new worker should register its process ID. */
   ASSERT_EQ(local_scheduler->local_scheduler_state->child_pids.size(), 1);
   ASSERT_EQ(local_scheduler->local_scheduler_state->workers.size(),
-            num_workers - 1);
+            static_cast<size_t>(num_workers - 1));
   /* Make sure the new worker connects to the local_scheduler scheduler. */
   new_client_connection(local_scheduler->loop,
                         local_scheduler->local_scheduler_fd,
                         (void *) local_scheduler->local_scheduler_state, 0);
   ASSERT_EQ(local_scheduler->local_scheduler_state->child_pids.size(), 1);
   ASSERT_EQ(local_scheduler->local_scheduler_state->workers.size(),
-            num_workers);
+            static_cast<size_t>(num_workers));
   /* Make sure that the new worker registers its process ID. */
   worker = local_scheduler->local_scheduler_state->workers.back();
   process_message(local_scheduler->local_scheduler_state->loop, worker->sock,
                   worker, 0);
   ASSERT_EQ(local_scheduler->local_scheduler_state->child_pids.size(), 0);
   ASSERT_EQ(local_scheduler->local_scheduler_state->workers.size(),
-            num_workers);
+            static_cast<size_t>(num_workers));
 
   /* Clean up. */
   close(new_worker_fd);
diff --git a/src/plasma/CMakeLists.txt b/src/plasma/CMakeLists.txt
index 1f09b683f39e..d3748ada43e6 100644
--- a/src/plasma/CMakeLists.txt
+++ b/src/plasma/CMakeLists.txt
@@ -12,7 +12,7 @@ find_package(Plasma)
 include_directories(SYSTEM ${PLASMA_INCLUDE_DIR})
 
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} --std=c99 -D_XOPEN_SOURCE=500 -D_POSIX_C_SOURCE=200809L -O3")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --std=c++11 -D_XOPEN_SOURCE=500 -D_POSIX_C_SOURCE=200809L -O3")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --std=c++11 -D_XOPEN_SOURCE=500 -D_POSIX_C_SOURCE=200809L -O3 -Werror -Wall")
 
 if(UNIX AND NOT APPLE)
   link_libraries(rt)
diff --git a/src/plasma/plasma_manager.cc b/src/plasma/plasma_manager.cc
index d771a1fc8ada..4ba80fb2db18 100644
--- a/src/plasma/plasma_manager.cc
+++ b/src/plasma/plasma_manager.cc
@@ -317,7 +317,6 @@ void add_wait_request_for_object(PlasmaManagerState *manager_state,
   auto &object_wait_requests =
       object_wait_requests_from_type(manager_state, type);
 
-  auto object_wait_requests_it = object_wait_requests.find(object_id);
   /* Add this wait request to the vector of wait requests involving this object
    * ID. Creates a vector of wait requests if none exist involving the object
    * ID. */
@@ -336,7 +335,7 @@ void remove_wait_request_for_object(PlasmaManagerState *manager_state,
    * vector. */
   if (object_wait_requests_it != object_wait_requests.end()) {
     std::vector<WaitRequest *> &wait_requests = object_wait_requests_it->second;
-    for (int i = 0; i < wait_requests.size(); ++i) {
+    for (size_t i = 0; i < wait_requests.size(); ++i) {
       if (wait_requests[i] == wait_req) {
         /* Remove the wait request from the array. */
         wait_requests.erase(wait_requests.begin() + i);
@@ -413,7 +412,7 @@ void update_object_wait_requests(PlasmaManagerState *manager_state,
         index += 1;
       }
     }
-    DCHECK(index == wait_requests.size());
+    DCHECK(static_cast<size_t>(index) == wait_requests.size());
     /* Remove the array of wait requests for this object, since no one should be
      * waiting for this object anymore. */
     object_wait_requests.erase(object_wait_requests_it);
@@ -862,7 +861,8 @@ void request_transfer_from(PlasmaManagerState *manager_state,
                            FetchRequest *fetch_req) {
   CHECK(fetch_req->manager_vector.size() > 0);
   CHECK(fetch_req->next_manager >= 0 &&
-        fetch_req->next_manager < fetch_req->manager_vector.size());
+        static_cast<size_t>(fetch_req->next_manager) <
+            fetch_req->manager_vector.size());
   char addr[16];
   int port;
   parse_ip_addr_port(fetch_req->manager_vector[fetch_req->next_manager].c_str(),
diff --git a/src/plasma/test/client_tests.cc b/src/plasma/test/client_tests.cc
index 5362483592e2..39e25828d07b 100644
--- a/src/plasma/test/client_tests.cc
+++ b/src/plasma/test/client_tests.cc
@@ -111,13 +111,13 @@ TEST plasma_fetch_tests(void) {
 }
 
 void init_data_123(uint8_t *data, uint64_t size, uint8_t base) {
-  for (int i = 0; i < size; i++) {
+  for (size_t i = 0; i < size; i++) {
     data[i] = base + i;
   }
 }
 
 bool is_equal_data_123(uint8_t *data1, uint8_t *data2, uint64_t size) {
-  for (int i = 0; i < size; i++) {
+  for (size_t i = 0; i < size; i++) {
     if (data1[i] != data2[i]) {
       return false;
     };