diff --git a/src/vim9compile.c b/src/vim9compile.c
index 5644c50..eb84e35 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1663,7 +1663,11 @@
 	++p;
 	while (*p != ')' && *p != NUL)
 	{
+	    char_u *sp = p;
+
 	    p = skip_type(p);
+	    if (p == sp)
+		return p;  // syntax error
 	    if (*p == ',')
 		p = skipwhite(p + 1);
 	}