diff --git a/src/keyboard.c b/src/keyboard.c
index 69e6b751c5fb26ae42e7db4448388a95074aec99..7eb9cf23717ed776886211d860bc96d175e41e33 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -44,7 +44,7 @@ getModifierMap (char *str)
     gchar *tmp;
     int map;
 
-    tmp = g_ascii_strdown ((gchar *) str, -1);
+    tmp = g_ascii_strdown ((gchar *) str, strlen (str));
     map = 0;
 
     if (strstr (tmp, "shift"))