diff --git a/lib/test.js b/lib/test.js
index be62ebb..6812255 100644
--- a/lib/test.js
+++ b/lib/test.js
@@ -78,7 +78,7 @@ function wrapAssertFn(assertFn) {
   return function(res) {
     var badStack;
     var err = assertFn(res);
-    if (err && err.stack) {
+    if (err instanceof Error && err.stack) {
       badStack = err.stack.replace(err.message, '').split('\n').slice(1);
       err.stack = [err.toString()]
         .concat(savedStack)
diff --git a/test/supertest.js b/test/supertest.js
index bdeb683..5f43893 100644
--- a/test/supertest.js
+++ b/test/supertest.js
@@ -738,6 +738,18 @@ describe('request(app)', function () {
           .end(done);
       });
 
+      it("doesn't create false negatives on non error objects", function (done) {
+        const handler = {
+          get: function(target, prop, receiver) {
+            throw Error('Should not be called for non Error objects');
+          }
+        };
+        const proxy = new Proxy({}, handler); // eslint-disable-line no-undef
+        get
+          .expect(() => proxy)
+          .end(done);
+      });
+
       it('handles multiple asserts', function (done) {
         const calls = [];
         get