diff --git a/src/os_win32.c b/src/os_win32.c
index 960943c..b0502b2 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -1521,7 +1521,12 @@
 #endif
 		   )
 		{
+#ifdef FEAT_MBYTE
+		    n = (*mb_char2bytes)(typeahead[typeaheadlen] | 0x80,
+						    typeahead + typeaheadlen);
+#else
 		    typeahead[typeaheadlen] |= 0x80;
+#endif
 		    modifiers &= ~MOD_MASK_ALT;
 		}