diff --git a/src/json.c b/src/json.c
index 9fb6af0..8674bf2 100644
--- a/src/json.c
+++ b/src/json.c
@@ -452,7 +452,12 @@
 		    nr = 0;
 		    len = 0;
 		    vim_str2nr(p + 2, NULL, &len,
-				     STR2NR_HEX + STR2NR_FORCE, &nr, NULL, 4);
+			     STR2NR_HEX + STR2NR_FORCE, &nr, NULL, 4, TRUE);
+		    if (len == 0)
+		    {
+			ga_clear(&ga);
+			return FAIL;
+		    }
 		    p += len + 2;
 		    if (0xd800 <= nr && nr <= 0xdfff
 			    && (int)(reader->js_end - p) >= 6
@@ -463,7 +468,12 @@
 			/* decode surrogate pair: \ud812\u3456 */
 			len = 0;
 			vim_str2nr(p + 2, NULL, &len,
-				     STR2NR_HEX + STR2NR_FORCE, &nr2, NULL, 4);
+			     STR2NR_HEX + STR2NR_FORCE, &nr2, NULL, 4, TRUE);
+			if (len == 0)
+			{
+			    ga_clear(&ga);
+			    return FAIL;
+			}
 			if (0xdc00 <= nr2 && nr2 <= 0xdfff)
 			{
 			    p += len + 2;
@@ -783,7 +793,13 @@
 
 			    vim_str2nr(reader->js_buf + reader->js_used,
 				    NULL, &len, 0, /* what */
-				    &nr, NULL, 0);
+				    &nr, NULL, 0, TRUE);
+			    if (len == 0)
+			    {
+				emsg(_(e_invarg));
+				retval = FAIL;
+				goto theend;
+			    }
 			    if (cur_item != NULL)
 			    {
 				cur_item->v_type = VAR_NUMBER;