diff --git a/examples/index.html b/examples/index.html
index 843006244..824d95c0a 100644
--- a/examples/index.html
+++ b/examples/index.html
@@ -14,4 +14,9 @@ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 -->
+<script>
+var msg = 'If an inconsistent behavior is found, please try to clear $GOPATH/pkg/*_js directory.' +
+  ' See also https://github.com/gopherjs/gopherjs/issues/440.';
+console.warn(msg);
+</script>
 <script src="main.js"></script>