diff --git a/src/vim9execute.c b/src/vim9execute.c
index 5251d48..3cb8628 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -653,7 +653,7 @@
 	    case ISN_EXECCONCAT:
 		{
 		    int	    count = iptr->isn_arg.number;
-		    int	    len = 0;
+		    size_t  len = 0;
 		    int	    pass;
 		    int	    i;
 		    char_u  *cmd = NULL;