diff --git a/include/propkeydef.h b/include/propkeydef.h
index 2a796eaf3c4..ab8a7e6db81 100644
--- a/include/propkeydef.h
+++ b/include/propkeydef.h
@@ -58,6 +58,9 @@
 #ifndef _PROPERTYKEY_EQUALITY_OPERATORS_
 #define _PROPERTYKEY_EQUALITY_OPERATORS_
 #ifdef __cplusplus
+extern "C++"
+{
+
 inline bool operator==(REFPROPERTYKEY guidOne, REFPROPERTYKEY guidOther)
 {
     return IsEqualPropertyKey(guidOne, guidOther);
@@ -66,5 +69,7 @@ inline bool operator!=(REFPROPERTYKEY guidOne, REFPROPERTYKEY guidOther)
 {
     return !(guidOne == guidOther);
 }
+
+}
 #endif
 #endif