diff --git a/spec/tests.js b/spec/tests.js
index 1537f1d..ec41a88 100644
--- a/spec/tests.js
+++ b/spec/tests.js
@@ -225,6 +225,12 @@ module.exports = [
         value1: {toString: ()=>'Hello world!'},
         value2: {toString: ()=>'Hi!'},
         equal: false
+      },
+      {
+        description: 'objects without `valueOf` and `toString` function do not throw error',
+        value1: Object.assign(Object.create(null), { a: 1 }),
+        value2: Object.assign(Object.create(null), { a: 1 }),
+        equal: true
       }
     ]
   },
@@ -397,4 +403,4 @@ module.exports = [
 ];
 
 function func1() {}
-function func2() {}
+function func2() {}
\ No newline at end of file
diff --git a/src/index.jst b/src/index.jst
index 5d4ee2f..e247aef 100644
--- a/src/index.jst
+++ b/src/index.jst
@@ -48,8 +48,8 @@ module.exports = function equal(a, b) {
 {{?}}
 
     if (a.constructor === RegExp) return a.source === b.source && a.flags === b.flags;
-    if (a.valueOf !== Object.prototype.valueOf) return a.valueOf() === b.valueOf();
-    if (a.toString !== Object.prototype.toString) return a.toString() === b.toString();
+    if (a.valueOf !== Object.prototype.valueOf && typeof a.valueOf === 'function' && typeof b.valueOf === 'function') return a.valueOf() === b.valueOf();
+    if (a.toString !== Object.prototype.toString && typeof a.toString === 'function' && typeof b.toString === 'function') return a.toString() === b.toString();
 
     keys = Object.keys(a);
     length = keys.length;