diff --git a/src/main.c b/src/main.c
index 66db3eb..78b6122 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4194,7 +4194,7 @@
 		size_t	len = STRLEN(cmd) + STRLEN(err) + 5;
 		char_u	*msg;
 
-		msg = alloc(len);
+		msg = alloc((unsigned)len);
 		if (msg != NULL)
 		    vim_snprintf((char *)msg, len, "%s: \"%s\"", err, cmd);
 		*result = msg;