--- a/ipc/mscom/StructStream.h
+++ b/ipc/mscom/StructStream.h
@@ -71,16 +71,21 @@ public:
     }
   }
 
   ~StructToStream()
   {
     if (mHandle) {
       ::MesHandleFree(mHandle);
     }
+    if (mBuffer) {
+      // Bug 1440564: You'd think that MesHandleFree would free the buffer,
+      // since it was created by RPC, but it doesn't.
+      midl_user_free(mBuffer);
+    }
   }
 
   static unsigned long GetEmptySize()
   {
     return sizeof(detail::EncodedLenT);
   }
 
   static HRESULT WriteEmpty(IStream* aDestStream)