diff --git a/src/state/targetState.ts b/src/state/targetState.ts
index d791105e..0a9ef524 100644
--- a/src/state/targetState.ts
+++ b/src/state/targetState.ts
@@ -3,7 +3,7 @@
 import { StateDeclaration, StateOrName, TargetStateDef } from './interface';
 import { TransitionOptions } from '../transition/interface';
 import { StateObject } from './stateObject';
-import { isString } from '../common/predicates';
+import { isObject, isString } from '../common/predicates';
 import { stringify } from '../common/strings';
 import { extend } from '../common';
 import { StateRegistry } from './stateRegistry';
@@ -44,7 +44,9 @@ export class TargetState {
   private _options: TransitionOptions;
 
   /** Returns true if the object has a state property that might be a state or state name */
-  static isDef = (obj): obj is TargetStateDef => obj && obj.state && (isString(obj.state) || isString(obj.state.name));
+  static isDef = (obj): obj is TargetStateDef => {
+    return obj && obj.state && (isString(obj.state) || (isObject(obj.state) && isString(obj.state.name)));
+  };
 
   /**
    * The TargetState constructor
diff --git a/test/targetStateSpec.ts b/test/targetStateSpec.ts
index 9c047d5a..d8460340 100644
--- a/test/targetStateSpec.ts
+++ b/test/targetStateSpec.ts
@@ -28,6 +28,18 @@ describe('TargetState object', function() {
     expect(ref.error()).toBe("No such state 'notfound'");
   });
 
+  describe('.isDef', function() {
+    it('should return true for TargetStateDef objects', () => {
+      expect(TargetState.isDef({ state: 'foo' })).toBeTrue();
+      expect(TargetState.isDef({ state: { name: 'foo' } })).toBeTrue();
+    });
+
+    it('should return false for TargetState instances', () => {
+      const ref = new TargetState(registry, 'foo');
+      expect(TargetState.isDef(ref)).toBeFalse();
+    });
+  });
+
   describe('.withState', function() {
     it('should replace the target state', () => {
       const ref = new TargetState(registry, 'foo');