diff --git a/src/_vendor/zod-to-json-schema/parseDef.ts b/src/_vendor/zod-to-json-schema/parseDef.ts
index f4dd747ca..fe0a0b6ff 100644
--- a/src/_vendor/zod-to-json-schema/parseDef.ts
+++ b/src/_vendor/zod-to-json-schema/parseDef.ts
@@ -131,7 +131,10 @@ const get$ref = (
     // `["#","definitions","contactPerson","properties","person1","properties","name"]`
     // then we'll extract it out to `contactPerson_properties_person1_properties_name`
     case 'extract-to-root':
-      const name = item.path.slice(refs.basePath.length + 1).join('_');
+      const name = item.path
+        .slice(refs.basePath.length + 1)
+        .map((segment) => segment.replace(/\s+/g, '_'))
+        .join('_');
 
       // we don't need to extract the root schema in this case, as it's already
       // been added to the definitions
diff --git a/tests/helpers/zod.test.ts b/tests/helpers/zod.test.ts
index 1bc766376..7c2faca93 100644
--- a/tests/helpers/zod.test.ts
+++ b/tests/helpers/zod.test.ts
@@ -359,4 +359,33 @@ describe.each([
 
     expect(consoleSpy).toHaveBeenCalledTimes(0);
   });
+
+  it('sanitizes property names with spaces in $ref values', () => {
+    const Thing = z.object({ id: z.string() });
+    const Root = z.object({
+      group: z.object({
+        'Thing With Spaces': Thing,
+        AnotherUsage: Thing,
+      }),
+    });
+
+    const result = zodResponseFormat(Root, 'example-scope');
+    const schema = result.json_schema.schema;
+
+    // Check definitions keys (draft-07 uses "definitions" not "$defs")
+    const defs = (schema as any).definitions || (schema as any).$defs || {};
+    const defsKeys = Object.keys(defs);
+    const defsWithSpaces = defsKeys.filter((key: string) => key.includes(' '));
+    expect(defsWithSpaces).toEqual([]);
+
+    // Check all $ref values don't contain spaces
+    const schemaStr = JSON.stringify(schema);
+    const refMatches = schemaStr.match(/"\$ref"\s*:\s*"([^"]+)"/g) || [];
+
+    refMatches.forEach((match) => {
+      const refValue = match.match(/"\$ref"\s*:\s*"([^"]+)"/)?.[1];
+      expect(refValue).toBeDefined();
+      expect(refValue).not.toContain(' ');
+    });
+  });
 });