diff --git a/modules/beast_core/streams/beast_MemoryInputStream.h b/modules/beast_core/streams/beast_MemoryInputStream.h
index d3e0d0b8d..038feab6e 100644
--- a/modules/beast_core/streams/beast_MemoryInputStream.h
+++ b/modules/beast_core/streams/beast_MemoryInputStream.h
@@ -53,7 +53,7 @@ public:
     */
     MemoryInputStream (const void* sourceData,
                        size_t sourceDataSize,
-                       bool keepInternalCopyOfData);
+                       bool keepInternalCopyOfData = false);
 
     /** Creates a MemoryInputStream.