diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000000..5659dfa757
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "parallel-hashmap"]
+	path = parallel-hashmap
+	url = https://github.com/greg7mdp/parallel-hashmap.git
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b8fdee7d3a..1e446508e5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -61,6 +61,8 @@ else()
 	endif()
 endif()
 
+include_directories(parallel-hashmap)
+
 # --- optional re2c
 set(RE2C_MAJOR_VERSION 0)
 find_program(RE2C re2c)
diff --git a/configure.py b/configure.py
index c88daad508..b2abdfd50a 100755
--- a/configure.py
+++ b/configure.py
@@ -345,6 +345,7 @@ def search_system_path(file_name: str) -> Optional[str]:  # type: ignore # Missi
               # Disable size_t -> int truncation warning.
               # We never have strings or arrays larger than 2**31.
               '/wd4267',
+              '/Iparallel-hashmap',
               '/DNOMINMAX', '/D_CRT_SECURE_NO_WARNINGS',
               '/D_HAS_EXCEPTIONS=0',
               '/DNINJA_PYTHON="%s"' % options.with_python]
@@ -363,6 +364,7 @@ def search_system_path(file_name: str) -> Optional[str]:  # type: ignore # Missi
               '-fno-exceptions',
               '-std=c++11',
               '-fvisibility=hidden', '-pipe',
+              '-Iparallel-hashmap',
               '-DNINJA_PYTHON="%s"' % options.with_python]
     if options.debug:
         cflags += ['-D_GLIBCXX_DEBUG', '-D_GLIBCXX_DEBUG_PEDANTIC']
diff --git a/parallel-hashmap b/parallel-hashmap
new file mode 160000
index 0000000000..d88c5e1507
--- /dev/null
+++ b/parallel-hashmap
@@ -0,0 +1 @@
+Subproject commit d88c5e15079047777b418132ece5879e7c9aaa2b
diff --git a/src/hash_map.h b/src/hash_map.h
index 3f465338ac..5448a3fcef 100644
--- a/src/hash_map.h
+++ b/src/hash_map.h
@@ -17,6 +17,8 @@
 
 #include <algorithm>
 #include <string.h>
+#include "parallel_hashmap/phmap.h"
+#include "parallel_hashmap/phmap_utils.h"
 #include "string_piece.h"
 #include "util.h"
 
@@ -53,8 +55,6 @@ unsigned int MurmurHash2(const void* key, size_t len) {
   return h;
 }
 
-#include <unordered_map>
-
 namespace std {
 template<>
 struct hash<StringPiece> {
@@ -73,7 +73,7 @@ struct hash<StringPiece> {
 /// mapping StringPiece => Foo*.
 template<typename V>
 struct ExternalStringHashMap {
-  typedef std::unordered_map<StringPiece, V> Type;
+  typedef phmap::flat_hash_map<StringPiece, V> Type;
 };
 
 #endif // NINJA_MAP_H_