diff --git a/src/cmdhist.c b/src/cmdhist.c
index 96a9b3e..6342f02 100644
--- a/src/cmdhist.c
+++ b/src/cmdhist.c
@@ -674,7 +674,7 @@
 	return;
 
     for ( ; *p; ++p)
-	if (STRNCMP(p, "key", 3) == 0 && !isalpha(p[3]))
+	if (STRNCMP(p, "key", 3) == 0 && !SAFE_isalpha(p[3]))
 	{
 	    p = vim_strchr(p + 3, '=');
 	    if (p == NULL)