diff --git a/src/json.c b/src/json.c
index d0a087a..4b9a2e8 100644
--- a/src/json.c
+++ b/src/json.c
@@ -1156,6 +1156,9 @@
 {
     js_read_T	reader;
 
+    if (in_vim9script() && check_for_string_arg(argvars, 0) == FAIL)
+	return;
+
     reader.js_buf = tv_get_string(&argvars[0]);
     reader.js_fill = NULL;
     reader.js_used = 0;
@@ -1181,6 +1184,9 @@
 {
     js_read_T	reader;
 
+    if (in_vim9script() && check_for_string_arg(argvars, 0) == FAIL)
+	return;
+
     reader.js_buf = tv_get_string(&argvars[0]);
     reader.js_fill = NULL;
     reader.js_used = 0;