diff --git a/app.js b/app.js
index 3404f614..a70ce300 100755
--- a/app.js
+++ b/app.js
@@ -455,7 +455,6 @@ function embeddedHandler(req, res, next) {
     res.end();
 }
 
-
 findCompilers()
     .then(function (compilers) {
         var prevCompilers;
diff --git a/static/alert.js b/static/alert.js
new file mode 100644
index 00000000..c18aadae
--- /dev/null
+++ b/static/alert.js
@@ -0,0 +1,41 @@
+// Copyright (c) 2012-2017, Matt Godbolt
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//     * Redistributions of source code must retain the above copyright notice,
+//       this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above copyright
+//       notice, this list of conditions and the following disclaimer in the
+//       documentation and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+
+define(function (require) {
+    var $ = require('jquery');
+
+    function Alert() {
+        this.modal = $('#alert');
+        this.title = this.modal.find('.modal-title');
+        this.body = this.modal.find('.modal-body');
+    }
+
+    Alert.prototype.alert = function (title, body) {
+        this.title.html(title);
+        this.body.html(body);
+        this.modal.modal();
+    };
+    return Alert;
+});
\ No newline at end of file
diff --git a/static/explorer.css b/static/explorer.css
index 0e76984f..4f24a673 100644
--- a/static/explorer.css
+++ b/static/explorer.css
@@ -213,4 +213,10 @@ pre.content {
 .compile-time {
     font-size: x-small;
     font-style: italic;
+}
+
+.url-parse-info {
+    font-size: small;
+    margin-top: 1em;
+    font-style: italic;
 }
\ No newline at end of file
diff --git a/static/index.html b/static/index.html
index 66372782..2eb68f66 100644
--- a/static/index.html
+++ b/static/index.html
@@ -243,5 +243,24 @@ int square(int num) {
     <!-- /.modal-dialog -->
 </div>
 
+<div class="modal fade gl_keep" id="alert">
+    <div class="modal-dialog">
+        <div class="modal-content">
+            <div class="modal-header">
+                <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
+                <h4 class="modal-title">Something alert worthy</h4>
+            </div>
+            <div class="modal-body">
+            </div>
+            <!-- model-body -->
+            <div class="modal-footer">
+                <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
+            </div>
+        </div>
+        <!-- /.modal-content -->
+    </div>
+    <!-- /.modal-dialog -->
+</div>
+
 </body>
 </html>
diff --git a/static/main.js b/static/main.js
index f95c5a82..32be49c2 100644
--- a/static/main.js
+++ b/static/main.js
@@ -64,6 +64,7 @@ define(function (require) {
     var clipboard = require('clipboard');
     var Hub = require('hub');
     var Raven = require('raven-js');
+    var Alert = require('alert');
 
     function start() {
         analytics.initialise();
@@ -71,6 +72,7 @@ define(function (require) {
 
         var options = require('options');
         $('.language-name').text(options.language);
+        var alert = new Alert();
 
         var safeLang = options.language.toLowerCase().replace(/[^a-z_]+/g, '');
         var defaultSrc = $('.template .lang.' + safeLang).text().trim();
@@ -87,7 +89,17 @@ define(function (require) {
 
         var config;
         if (!options.embedded) {
-            config = url.deserialiseState(window.location.hash.substr(1));
+            var serializedState = window.location.hash.substr(1);
+            if (serializedState) {
+                try {
+                    config = url.deserialiseState(serializedState);
+                } catch (exception) {
+                    alert.alert("Unable to parse URL",
+                        "<div>Compiler Explorer was unable to parse the URL hash. " +
+                        "Please check it and try again.</div>" +
+                        "<div class='url-parse-info'>" + exception + "</div>");
+                }
+            }
             if (config) {
                 // replace anything in the default config with that from the hash
                 config = _.extend(defaultConfig, config);
diff --git a/static/url.js b/static/url.js
index 1c0bdda5..967ea402 100644
--- a/static/url.js
+++ b/static/url.js
@@ -34,7 +34,7 @@ define(function (require) {
 
     function convertOldState(state) {
         var sc = state.compilers[0];
-        if (!sc) return false;
+        if (!sc) throw new Error("Unable to determine compiler from old state");
         var content = [];
         var source;
         if (sc.sourcez) {
@@ -68,7 +68,7 @@ define(function (require) {
                 state = GoldenLayout.unminifyConfig(state);
                 break;
             default:
-                return false;
+                throw new Error("Invalid version '" + state.version + "'");
         }
         return state;
     }
@@ -83,21 +83,24 @@ define(function (require) {
 
     function deserialiseState(stateText) {
         var state;
+        var exception;
         try {
             state = unrisonify(stateText);
             if (state && state.z) {
                 state = unrisonify(lzstring.decompressFromBase64(state.z));
             }
-        } catch (ignored) {
+        } catch (ex) {
+            exception = ex;
         }
 
-
         if (!state) {
             try {
                 state = $.parseJSON(decodeURIComponent(stateText));
-            } catch (ignored) {
+            } catch (ex) {
+                if (!exception) exception = ex;
             }
         }
+        if (!state && exception) throw exception;
         return loadState(state);
     }