diff --git a/grammars/json.gbnf b/grammars/json.gbnf
index a8a80752e..2b370ef64 100644
--- a/grammars/json.gbnf
+++ b/grammars/json.gbnf
@@ -16,10 +16,10 @@ array  ::=
 string ::=
   "\"" (
     [^"\\\x7F\x00-\x1F] |
-    "\\" (["\\/bfnrt] | "u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F]) # escapes
+    "\\" (["\\bfnrt] | "u" [0-9a-fA-F]{4}) # escapes
   )* "\"" ws
 
-number ::= ("-"? ([0-9] | [1-9] [0-9]*)) ("." [0-9]+)? ([eE] [-+]? [0-9]+)? ws
+number ::= ("-"? ([0-9] | [1-9] [0-9]{0,15})) ("." [0-9]+)? ([eE] [-+]? [0-9] [1-9]{0,15})? ws
 
 # Optional space: by convention, applied in this grammar after literal chars when allowed
-ws ::= ([ \t\n] ws)?
+ws ::= [ \t\n]{,20}
diff --git a/grammars/json_arr.gbnf b/grammars/json_arr.gbnf
index 31a3202f8..d85fc23db 100644
--- a/grammars/json_arr.gbnf
+++ b/grammars/json_arr.gbnf
@@ -25,10 +25,10 @@ array  ::=
 string ::=
   "\"" (
     [^"\\\x7F\x00-\x1F] |
-    "\\" (["\\/bfnrt] | "u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F]) # escapes
+    "\\" (["\\bfnrt] | "u" [0-9a-fA-F]{4}) # escapes
   )* "\"" ws
 
-number ::= ("-"? ([0-9] | [1-9] [0-9]*)) ("." [0-9]+)? ([eE] [-+]? [0-9]+)? ws
+number ::= ("-"? ([0-9] | [1-9] [0-9]{0,15})) ("." [0-9]+)? ([eE] [-+]? [1-9] [0-9]{0,15})? ws
 
 # Optional space: by convention, applied in this grammar after literal chars when allowed
-ws ::= ([ \t\n] ws)?
+ws ::= [ \t\n]{,20}