diff --git a/common/json-schema-to-grammar.cpp b/common/json-schema-to-grammar.cpp
index 4d2c36d88..fe41c7295 100644
--- a/common/json-schema-to-grammar.cpp
+++ b/common/json-schema-to-grammar.cpp
@@ -214,7 +214,7 @@ std::string not_strings(const std::vector<std::string> & strings) {
     };
     visit(trie);
 
-    out << " ) char* [\"]";
+    out << " ) char* [\"] space";
     return out.str();
 }
 
diff --git a/examples/json_schema_to_grammar.py b/examples/json_schema_to_grammar.py
index 67ae921c0..252d63fd2 100755
--- a/examples/json_schema_to_grammar.py
+++ b/examples/json_schema_to_grammar.py
@@ -71,6 +71,47 @@ NON_LITERAL_SET = set('|.()[]{}*+?')
 ESCAPED_IN_REGEXPS_BUT_NOT_IN_LITERALS = set('[]()|{}*+?')
 
 
+def not_strings(strings):
+    class TrieNode:
+        def __init__(self):
+            self.children = {}
+            self.is_end_of_string = False
+
+        def insert(self, string):
+            node = self
+            for c in string:
+                node = node.children.setdefault(c, TrieNode())
+            node.is_end_of_string = True
+
+    trie = TrieNode()
+    for s in strings:
+        trie.insert(s)
+
+    out = ['["] ( ']
+
+    def visit(node):
+        rejects = []
+        first = True
+        for c, child in node.children.items():
+            rejects.append(c)
+            if child.is_end_of_string:
+                continue
+            if first:
+                first = False
+            else:
+                out.append(' | ')
+            out.append(f'[{c}] (')
+            visit(child)
+            out.append(')')
+        if node.children:
+            if not first:
+                out.append(' | ')
+            out.append(f'[^"{"".join(rejects)}]')
+    visit(trie)
+
+    out.append(' ) char* ["] space')
+    return ''.join(out)
+
 class SchemaConverter:
     def __init__(self, *, prop_order, allow_fetch, dotall, raw_pattern):
         self._prop_order = prop_order
@@ -471,9 +512,12 @@ class SchemaConverter:
         if additional_properties == True or isinstance(additional_properties, dict):
             sub_name = f'{name}{"-" if name else ""}additional'
             value_rule = self.visit({} if additional_properties == True else additional_properties, f'{sub_name}-value')
+            key_rule = self._add_primitive('string', PRIMITIVE_RULES['string']) if not sorted_props \
+                else self._add_rule(f'{sub_name}-k', not_strings(sorted_props))
+            
             prop_kv_rule_names["*"] = self._add_rule(
                 f'{sub_name}-kv',
-                self._add_primitive('string', PRIMITIVE_RULES['string']) + f' ":" space {value_rule}'
+                f'{key_rule} ":" space {value_rule}'
             )
             optional_props.append("*")
 
diff --git a/tests/test-json-schema-to-grammar.cpp b/tests/test-json-schema-to-grammar.cpp
index 9fa704c5e..2da6b88e9 100755
--- a/tests/test-json-schema-to-grammar.cpp
+++ b/tests/test-json-schema-to-grammar.cpp
@@ -634,7 +634,7 @@ static void test_all(const std::string & lang, std::function<void(const TestCase
         })""",
         R"""(
             a-kv ::= "\"a\"" space ":" space number
-            additional-k ::= ["] ( [^"a] ) char* ["]
+            additional-k ::= ["] ( [^"a] ) char* ["] space
             additional-kv ::= additional-k ":" space string
             char ::= [^"\\\x7F\x00-\x1F] | [\\] (["\\bfnrt] | "u" [0-9a-fA-F]{4})
             decimal-part ::= [0-9]{1,16}
@@ -659,7 +659,7 @@ static void test_all(const std::string & lang, std::function<void(const TestCase
         R"""(
             a-kv ::= "\"a\"" space ":" space number
             a-rest ::= ( "," space additional-kv )*
-            additional-k ::= ["] ( [^"a] ) char* ["]
+            additional-k ::= ["] ( [^"a] ) char* ["] space
             additional-kv ::= additional-k ":" space number
             decimal-part ::= [0-9]{1,16}
             integral-part ::= [0] | [1-9] [0-9]{0,15}
@@ -682,7 +682,7 @@ static void test_all(const std::string & lang, std::function<void(const TestCase
             "additionalProperties": {"type": "number"}
         })""",
         R"""(
-            additional-k ::= ["] ( [a] ([l] ([s] ([^"o]) | [^"s]) | [n] ([^"d]) | [^"ln]) | [^"a] ) char* ["]
+            additional-k ::= ["] ( [a] ([l] ([s] ([^"o]) | [^"s]) | [n] ([^"d]) | [^"ln]) | [^"a] ) char* ["] space
             additional-kv ::= additional-k ":" space number
             also-kv ::= "\"also\"" space ":" space number
             also-rest ::= ( "," space additional-kv )*
@@ -748,7 +748,7 @@ static void test_all(const std::string & lang, std::function<void(const TestCase
             alternative-1 ::= bar
             array ::= "[" space ( value ("," space value)* )? "]" space
             bar ::= "{" space  (bar-b-kv bar-b-rest | bar-additional-kv ( "," space bar-additional-kv )* )? "}" space
-            bar-additional-k ::= ["] ( [^"b] ) char* ["]
+            bar-additional-k ::= ["] ( [^"b] ) char* ["] space
             bar-additional-kv ::= bar-additional-k ":" space bar-additional-value
             bar-additional-value ::= object
             bar-b-kv ::= "\"b\"" space ":" space number
@@ -759,7 +759,7 @@ static void test_all(const std::string & lang, std::function<void(const TestCase
             foo ::= "{" space  (foo-a-kv foo-a-rest | foo-additional-kv ( "," space foo-additional-kv )* )? "}" space
             foo-a-kv ::= "\"a\"" space ":" space number
             foo-a-rest ::= ( "," space foo-additional-kv )*
-            foo-additional-k ::= ["] ( [^"a] ) char* ["]
+            foo-additional-k ::= ["] ( [^"a] ) char* ["] space
             foo-additional-kv ::= foo-additional-k ":" space foo-additional-value
             foo-additional-value ::= object
             integral-part ::= [0] | [1-9] [0-9]{0,15}