diff --git a/src/google/protobuf/map.h b/src/google/protobuf/map.h
index 9af782c922..4c5f64aa99 100644
--- a/src/google/protobuf/map.h
+++ b/src/google/protobuf/map.h
@@ -559,7 +559,7 @@ class PROTOBUF_EXPORT UntypedMapBase {
 
  protected:
   // 16 bytes is the minimum useful size for the array cache in the arena.
-  constexpr static map_index_t kMinTableSize = 16 / sizeof(void*);
+  enum : map_index_t { kMinTableSize = 16 / sizeof(void*) };
 
  public:
   Arena* arena() const { return this->alloc_.arena(); }