diff --git a/src/google/protobuf/stubs/bytestream.h b/src/google/protobuf/stubs/bytestream.h
index b9b43db0a8..cfa19f2965 100644
--- a/src/google/protobuf/stubs/bytestream.h
+++ b/src/google/protobuf/stubs/bytestream.h
@@ -57,7 +57,6 @@
 #include <google/protobuf/stubs/stringpiece.h>
 
 class CordByteSink;
-class MemBlock;
 
 namespace google {
 namespace protobuf {