diff --git a/grammars/json.gbnf b/grammars/json.gbnf
index a9537cdf9..a8a80752e 100644
--- a/grammars/json.gbnf
+++ b/grammars/json.gbnf
@@ -15,7 +15,7 @@ array  ::=
 
 string ::=
   "\"" (
-    [^"\\] |
+    [^"\\\x7F\x00-\x1F] |
     "\\" (["\\/bfnrt] | "u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F]) # escapes
   )* "\"" ws
 
diff --git a/grammars/json_arr.gbnf b/grammars/json_arr.gbnf
index ef53e77a0..31a3202f8 100644
--- a/grammars/json_arr.gbnf
+++ b/grammars/json_arr.gbnf
@@ -24,7 +24,7 @@ array  ::=
 
 string ::=
   "\"" (
-    [^"\\] |
+    [^"\\\x7F\x00-\x1F] |
     "\\" (["\\/bfnrt] | "u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F]) # escapes
   )* "\"" ws