diff --git a/src/longRunningCalls/longRunningApiCaller.ts b/src/longRunningCalls/longRunningApiCaller.ts
index 32d2fa612..f41bfb4ca 100644
--- a/src/longRunningCalls/longRunningApiCaller.ts
+++ b/src/longRunningCalls/longRunningApiCaller.ts
@@ -41,7 +41,7 @@ import {
 } from '../gax';
 import {GoogleError} from '../googleError';
 
-import {Operation} from './longrunning';
+import {Operation, LROOperation} from './longrunning';
 import {LongRunningDescriptor} from './longRunningDescriptor';
 
 export class LongrunningApiCaller implements APICaller {
@@ -105,7 +105,7 @@ export class LongrunningApiCaller implements APICaller {
         }
 
         const operation = new Operation(
-          rawResponse as Operation,
+          rawResponse as LROOperation,
           longrunningDescriptor,
           backoffSettings!,
           settings
diff --git a/src/longRunningCalls/longRunningDescriptor.ts b/src/longRunningCalls/longRunningDescriptor.ts
index e93543256..285ff59ce 100644
--- a/src/longRunningCalls/longRunningDescriptor.ts
+++ b/src/longRunningCalls/longRunningDescriptor.ts
@@ -29,18 +29,18 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+import * as protobuf from 'protobufjs';
 import {Descriptor} from '../descriptor';
 import {CallSettings} from '../gax';
 import {Metadata} from '../grpc';
 import {OperationsClient} from '../operationsClient';
-
 import {LongrunningApiCaller} from './longRunningApiCaller';
 
 /**
  * A callback to upack a google.protobuf.Any message.
  */
 export interface AnyDecoder {
-  (message: {}): Metadata;
+  (reader: protobuf.Reader | Uint8Array, length?: number): protobuf.Message<{}>;
 }
 
 /**
diff --git a/src/longRunningCalls/longrunning.ts b/src/longRunningCalls/longrunning.ts
index 6ab0feb5f..3069601a6 100644
--- a/src/longRunningCalls/longrunning.ts
+++ b/src/longRunningCalls/longrunning.ts
@@ -36,8 +36,7 @@ import {GaxCallPromise, ResultTuple} from '../apitypes';
 import {CancellablePromise} from '../call';
 import {BackoffSettings, CallOptions} from '../gax';
 import {GoogleError} from '../googleError';
-import {Metadata, MetadataValue} from '../grpc';
-
+import {Metadata} from '../grpc';
 import {LongRunningDescriptor} from './longRunningDescriptor';
 
 /**
@@ -52,14 +51,25 @@ export interface GetOperationCallback {
     err?: Error | null,
     result?: {},
     metadata?: {},
-    rawResponse?: Operation
+    rawResponse?: LROOperation
   ): void;
 }
 
+// This interface is essentially the TypeScript representation of google.longrunning.Operation.
+// TODO: we'll replace it with the proper type generated by `pbts`.
+export interface LROOperation {
+  name: string;
+  metadata: {value: Uint8Array};
+  done: boolean;
+  result: string;
+  error: GoogleError;
+  response: {value: Uint8Array};
+}
+
 export class Operation extends EventEmitter {
   completeListeners: number;
   hasActiveListeners: boolean;
-  latestResponse: Operation;
+  latestResponse: LROOperation;
   longrunningDescriptor: LongRunningDescriptor;
   result: {} | null;
   metadata: Metadata | null;
@@ -69,7 +79,7 @@ export class Operation extends EventEmitter {
   name?: string;
   done?: boolean;
   error?: GoogleError;
-  response?: {value: {}};
+  response?: {};
 
   /**
    * Wrapper for a google.longrunnung.Operation.
@@ -85,7 +95,7 @@ export class Operation extends EventEmitter {
    * requests.
    */
   constructor(
-    grpcOp: Operation,
+    grpcOp: LROOperation,
     longrunningDescriptor: LongRunningDescriptor,
     backoffSettings: BackoffSettings,
     callOptions?: CallOptions
@@ -201,8 +211,8 @@ export class Operation extends EventEmitter {
     );
 
     const noCallbackPromise = this.currentCallPromise_!.then(responses => {
-      self.latestResponse = responses[0] as Operation;
-      self._unpackResponse(responses[0] as Operation, callback);
+      self.latestResponse = responses[0] as LROOperation;
+      self._unpackResponse(responses[0] as LROOperation, callback);
       return promisifyResponse()!;
     });
 
@@ -211,7 +221,7 @@ export class Operation extends EventEmitter {
     }
   }
 
-  _unpackResponse(op: Operation, callback?: GetOperationCallback) {
+  _unpackResponse(op: LROOperation, callback?: GetOperationCallback) {
     const responseDecoder = this.longrunningDescriptor.responseDecoder;
     const metadataDecoder = this.longrunningDescriptor.metadataDecoder;
     let response: {};
@@ -237,7 +247,7 @@ export class Operation extends EventEmitter {
     }
 
     if (metadataDecoder && op.metadata) {
-      metadata = metadataDecoder(op.metadata.value);
+      metadata = (metadataDecoder(op.metadata.value) as unknown) as Metadata;
       this.metadata = metadata;
     }
     if (callback) {
@@ -265,7 +275,7 @@ export class Operation extends EventEmitter {
     if (this.backoffSettings.totalTimeoutMillis) {
       deadline = now.getTime() + this.backoffSettings.totalTimeoutMillis;
     }
-    let previousMetadataBytes: MetadataValue;
+    let previousMetadataBytes: Uint8Array;
     if (this.latestResponse.metadata) {
       previousMetadataBytes = this.latestResponse.metadata.value;
     }
@@ -378,7 +388,7 @@ export class Operation extends EventEmitter {
  * requests.
  */
 export function operation(
-  op: Operation,
+  op: LROOperation,
   longrunningDescriptor: LongRunningDescriptor,
   backoffSettings: BackoffSettings,
   callOptions?: CallOptions
diff --git a/test/unit/longrunning.ts b/test/unit/longrunning.ts
index 87f3a86bd..18c100287 100644
--- a/test/unit/longrunning.ts
+++ b/test/unit/longrunning.ts
@@ -205,7 +205,7 @@ describe('longrunning', () => {
         totalTimeoutMillis
       );
       const operation = longrunning.operation(
-        (SUCCESSFUL_OP as {}) as longrunning.Operation,
+        (SUCCESSFUL_OP as {}) as longrunning.LROOperation,
         desc,
         backoff
       );
@@ -488,7 +488,7 @@ describe('longrunning', () => {
           return promise;
         }
         const operation = longrunning.operation(
-          (SUCCESSFUL_OP as {}) as longrunning.Operation,
+          (SUCCESSFUL_OP as {}) as longrunning.LROOperation,
           desc,
           backoff,
           {