diff --git a/index.js b/index.js
index 22e1d341..2507f10a 100644
--- a/index.js
+++ b/index.js
@@ -438,7 +438,7 @@ function cloneOriginSchema (context, schema, schemaId) {
   for (const key in schema) {
     let value = schema[key]
 
-    if (key === '$ref' && value.charAt(0) === '#') {
+    if (key === '$ref' && typeof value === 'string' && value.charAt(0) === '#') {
       value = schemaId + value
     }
 
diff --git a/test/allof.test.js b/test/allof.test.js
index 4c5e3ba5..5c80873d 100644
--- a/test/allof.test.js
+++ b/test/allof.test.js
@@ -717,3 +717,39 @@ test('external recursive allOfs', (t) => {
   const stringify = build(schema, { schema: { externalSchema } })
   t.equal(stringify(data), '{"a":{"bar":"42","foo":{}},"b":{"bar":"42","foo":{}}}')
 })
+
+test('do not crash with $ref prop', (t) => {
+  t.plan(1)
+
+  const schema = {
+    title: 'object with $ref',
+    type: 'object',
+    properties: {
+      outside: {
+        $ref: '#/$defs/outside'
+      }
+    },
+    $defs: {
+      inside: {
+        type: 'object',
+        properties: {
+          $ref: {
+            type: 'string'
+          }
+        }
+      },
+      outside: {
+        allOf: [{
+          $ref: '#/$defs/inside'
+        }]
+      }
+    }
+  }
+  const stringify = build(schema)
+  const value = stringify({
+    outside: {
+      $ref: 'true'
+    }
+  })
+  t.equal(value, '{"outside":{"$ref":"true"}}')
+})