diff --git a/src/msw/registry.cpp b/src/msw/registry.cpp
index 0825e131fc..eb666c56f8 100644
--- a/src/msw/registry.cpp
+++ b/src/msw/registry.cpp
@@ -68,6 +68,10 @@ typedef BYTE* RegBinary;
     #define HKEY_DYN_DATA ((HKEY)0x80000006)
 #endif
 
+#ifndef KEY_WOW64_64KEY
+    #define KEY_WOW64_64KEY 0x0100
+#endif
+
 // ----------------------------------------------------------------------------
 // constants
 // ----------------------------------------------------------------------------