diff --git a/src/os_mswin.c b/src/os_mswin.c
index 9767a5b..3d74bdc 100644
--- a/src/os_mswin.c
+++ b/src/os_mswin.c
@@ -114,6 +114,7 @@
 typedef int TEXTMETRIC;
 typedef int UINT;
 typedef int WCHAR;
+typedef int WNDENUMPROC;
 typedef int WORD;
 typedef int WPARAM;
 typedef void VOID;