diff --git a/IPython/html/static/notebook/js/cell.js b/IPython/html/static/notebook/js/cell.js
index 9e2aac1..26ecbd2 100644
--- a/IPython/html/static/notebook/js/cell.js
+++ b/IPython/html/static/notebook/js/cell.js
@@ -53,7 +53,9 @@ define([
             get: function() { return that._metadata; },
             set: function(value) {
                 that._metadata = value;
-                that.celltoolbar.rebuild();
+                if (that.celltoolbar) {
+                    that.celltoolbar.rebuild();
+                }
             }
         });
 
@@ -194,11 +196,11 @@ define([
         if((cur.line !== 0 || cur.ch !==0) && event.keyCode === 38){
             event._ipkmIgnore = true;
         }
-        var nLastLine = editor.lastLine()
-        if(    ( event.keyCode === 40)
-            && (( cur.line !== nLastLine)
-            ||  ( cur.ch   !== editor.getLineHandle(nLastLine).text.length))
-          ){
+        var nLastLine = editor.lastLine();
+        if ((event.keyCode === 40) &&
+             ((cur.line !== nLastLine) ||
+               (cur.ch !== editor.getLineHandle(nLastLine).text.length))
+           ) {
             event._ipkmIgnore = true;
         }
         // if this is an edit_shortcuts shortcut, the global keyboard/shortcut
@@ -255,6 +257,14 @@ define([
     };
 
     /**
+     * should be overritten by subclass
+     * @method execute
+     */
+    Cell.prototype.execute = function () {
+        return;
+    };
+
+    /**
      * handle cell level logic when a cell is rendered
      * @method render
      * @return is the action being taken
@@ -386,7 +396,9 @@ define([
      * @method refresh
      */
     Cell.prototype.refresh = function () {
-        this.code_mirror.refresh();
+        if (this.code_mirror) {
+            this.code_mirror.refresh();
+        }
     };
 
     /**
@@ -590,8 +602,61 @@ define([
         this.code_mirror.setOption('mode', default_mode);
     };
 
+    var UnrecognizedCell = function (options) {
+        /** Constructor for unrecognized cells */
+        Cell.apply(this, arguments);
+        this.cell_type = 'unrecognized';
+        this.celltoolbar = null;
+        this.data = {};
+        
+        Object.seal(this);
+    };
+
+    UnrecognizedCell.prototype = Object.create(Cell.prototype);
+    
+    
+    // cannot merge or split unrecognized cells
+    UnrecognizedCell.prototype.is_mergeable = function () {
+        return false;
+    };
+    
+    UnrecognizedCell.prototype.is_splittable = function () {
+        return false;
+    };
+    
+    UnrecognizedCell.prototype.toJSON = function () {
+        // deepcopy the metadata so copied cells don't share the same object
+        return JSON.parse(JSON.stringify(this.data));
+    };
+
+    UnrecognizedCell.prototype.fromJSON = function (data) {
+        this.data = data;
+        if (data.metadata !== undefined) {
+            this.metadata = data.metadata;
+        } else {
+            data.metadata = this.metadata;
+        }
+        this.element.find('.inner_cell').text("Unrecognized cell type: " + data.cell_type);
+    };
+    
+    UnrecognizedCell.prototype.create_element = function () {
+        Cell.prototype.create_element.apply(this, arguments);
+        var cell = this.element = $("<div>").addClass('cell unrecognized_cell');
+        cell.attr('tabindex','2');
+
+        var prompt = $('<div/>').addClass('prompt input_prompt');
+        cell.append(prompt);
+        var inner_cell = $('<div/>').addClass('inner_cell');
+        inner_cell.text("Unrecognized cell type");
+        cell.append(inner_cell);
+        this.element = cell;
+    };
+
     // Backwards compatibility.
     IPython.Cell = Cell;
 
-    return {'Cell': Cell};
+    return {
+        Cell: Cell,
+        UnrecognizedCell: UnrecognizedCell
+    };
 });
diff --git a/IPython/html/static/notebook/js/notebook.js b/IPython/html/static/notebook/js/notebook.js
index 5bd4315..9bb3b00 100644
--- a/IPython/html/static/notebook/js/notebook.js
+++ b/IPython/html/static/notebook/js/notebook.js
@@ -6,6 +6,7 @@ define([
     'jquery',
     'base/js/utils',
     'base/js/dialog',
+    'notebook/js/cell',
     'notebook/js/textcell',
     'notebook/js/codecell',
     'services/sessions/session',
@@ -22,13 +23,14 @@ define([
     'notebook/js/scrollmanager'
 ], function (
     IPython, 
-    $, 
-    utils, 
-    dialog, 
-    textcell, 
-    codecell, 
+    $,
+    utils,
+    dialog,
+    cellmod,
+    textcell,
+    codecell,
     session, 
-    celltoolbar, 
+    celltoolbar,
     marked,
     CodeMirror,
     runMode,
@@ -894,7 +896,8 @@ define([
                 cell = new textcell.RawCell(cell_options);
                 break;
             default:
-                console.log("invalid cell type: ", type);
+                console.log("Unrecognized cell type: ", type, cellmod);
+                cell = new cellmod.UnrecognizedCell(cell_options);
             }
 
             if(this._insert_element_at_index(cell.element,index)) {
diff --git a/IPython/html/static/notebook/js/outputarea.js b/IPython/html/static/notebook/js/outputarea.js
index ae56b94..55bac95 100644
--- a/IPython/html/static/notebook/js/outputarea.js
+++ b/IPython/html/static/notebook/js/outputarea.js
@@ -245,7 +245,7 @@ define([
         'text/plain'
     ];
 
-    OutputArea.prototype.validate_output = function (json) {
+    OutputArea.prototype.validate_mimebundle = function (json) {
         // scrub invalid outputs
         var data = json.data;
         $.map(OutputArea.output_types, function(key){
@@ -263,11 +263,6 @@ define([
     OutputArea.prototype.append_output = function (json) {
         this.expand();
         
-        // validate output data types
-        if (json.data) {
-            json = this.validate_output(json);
-        }
-
         // Clear the output if clear is queued.
         var needs_height_reset = false;
         if (this.clear_queued) {
@@ -276,14 +271,26 @@ define([
         }
 
         var record_output = true;
-
-        if (json.output_type === 'execute_result') {
-            this.append_execute_result(json);
-        } else if (json.output_type === 'error') {
-            this.append_error(json);
-        } else if (json.output_type === 'stream') {
-            // append_stream might have merged the output with earlier stream output
-            record_output = this.append_stream(json);
+        console.log("appending", json);
+        switch(json.output_type) {
+            case 'execute_result':
+                json = this.validate_mimebundle(json);
+                this.append_execute_result(json);
+                break;
+            case 'stream':
+                // append_stream might have merged the output with earlier stream output
+                record_output = this.append_stream(json);
+                break;
+            case 'error':
+                this.append_error(json);
+                break;
+            case 'display_data':
+                // append handled below
+                json = this.validate_mimebundle(json);
+                break;
+            default:
+                console.log("unrecognized output type: " + json.output_type);
+                this.append_unrecognized(json);
         }
 
         // We must release the animation fixed height in a callback since Gecko
@@ -482,6 +489,15 @@ define([
     };
 
 
+    OutputArea.prototype.append_unrecognized = function (json) {
+        var toinsert = this.create_output_area();
+        var subarea = $('<div/>').addClass('output_subarea output_unrecognized');
+        toinsert.append(subarea);
+        subarea.text("Unrecognized output: " + json.output_type);
+        this._safe_append(toinsert);
+    };
+
+
     OutputArea.prototype.append_display_data = function (json, handle_inserted) {
         var toinsert = this.create_output_area();
         if (this.append_mime_type(json, toinsert, handle_inserted)) {
diff --git a/IPython/html/static/notebook/js/textcell.js b/IPython/html/static/notebook/js/textcell.js
index 24bd1e4..fb466b7 100644
--- a/IPython/html/static/notebook/js/textcell.js
+++ b/IPython/html/static/notebook/js/textcell.js
@@ -340,7 +340,7 @@ define([
     var textcell = {
         TextCell: TextCell,
         MarkdownCell: MarkdownCell,
-        RawCell: RawCell,
+        RawCell: RawCell
     };
     return textcell;
 });
diff --git a/IPython/html/static/notebook/less/cell.less b/IPython/html/static/notebook/less/cell.less
index 8bf3f85..1a5c541 100644
--- a/IPython/html/static/notebook/less/cell.less
+++ b/IPython/html/static/notebook/less/cell.less
@@ -61,3 +61,24 @@ div.prompt:empty {
     padding-top: 0;
     padding-bottom: 0;
 }
+
+div.unrecognized_cell {
+    // from text_cell
+    padding: 5px 5px 5px 0px;
+    .hbox();
+    
+    .inner_cell {
+        .border-radius(@border-radius-base);
+        padding: 5px;
+        font-weight: bold;
+        color: red;
+        border: 1px solid @light_border_color;
+        background: darken(@cell_background, 5%);
+    }
+}
+@media (max-width: 480px) {
+    // remove prompt indentation on small screens
+    div.unrecognized_cell > div.prompt {
+        display: none;
+    }
+}
diff --git a/IPython/html/static/notebook/less/outputarea.less b/IPython/html/static/notebook/less/outputarea.less
index 033359b..a9f15ed 100644
--- a/IPython/html/static/notebook/less/outputarea.less
+++ b/IPython/html/static/notebook/less/outputarea.less
@@ -172,3 +172,9 @@ input.raw_input:focus {
 p.p-space {
     margin-bottom: 10px;
 }
+
+div.output_unrecognized {
+  padding: 5px;
+  font-weight: bold;
+  color: red;
+}
\ No newline at end of file
diff --git a/IPython/html/static/style/ipython.min.css b/IPython/html/static/style/ipython.min.css
index 09e2df2..0acc29b 100644
--- a/IPython/html/static/style/ipython.min.css
+++ b/IPython/html/static/style/ipython.min.css
@@ -419,6 +419,36 @@ div.prompt:empty {
   padding-top: 0;
   padding-bottom: 0;
 }
+div.unrecognized_cell {
+  padding: 5px 5px 5px 0px;
+  /* Old browsers */
+  display: -webkit-box;
+  -webkit-box-orient: horizontal;
+  -webkit-box-align: stretch;
+  display: -moz-box;
+  -moz-box-orient: horizontal;
+  -moz-box-align: stretch;
+  display: box;
+  box-orient: horizontal;
+  box-align: stretch;
+  /* Modern browsers */
+  display: flex;
+  flex-direction: row;
+  align-items: stretch;
+}
+div.unrecognized_cell .inner_cell {
+  border-radius: 4px;
+  padding: 5px;
+  font-weight: bold;
+  color: red;
+  border: 1px solid #cfcfcf;
+  background: #eaeaea;
+}
+@media (max-width: 480px) {
+  div.unrecognized_cell > div.prompt {
+    display: none;
+  }
+}
 /* any special styling for code cells that are currently running goes here */
 div.input {
   page-break-inside: avoid;
@@ -888,6 +918,12 @@ input.raw_input:focus {
 p.p-space {
   margin-bottom: 10px;
 }
+div.output_unrecognized {
+  border-radius: 4px;
+  padding: 5px;
+  font-weight: bold;
+  color: red;
+}
 .rendered_html {
   color: #000000;
   /* any extras will just be numbers: */
diff --git a/IPython/html/static/style/style.min.css b/IPython/html/static/style/style.min.css
index 2430e1f..f0b94db 100644
--- a/IPython/html/static/style/style.min.css
+++ b/IPython/html/static/style/style.min.css
@@ -8288,6 +8288,36 @@ div.prompt:empty {
   padding-top: 0;
   padding-bottom: 0;
 }
+div.unrecognized_cell {
+  padding: 5px 5px 5px 0px;
+  /* Old browsers */
+  display: -webkit-box;
+  -webkit-box-orient: horizontal;
+  -webkit-box-align: stretch;
+  display: -moz-box;
+  -moz-box-orient: horizontal;
+  -moz-box-align: stretch;
+  display: box;
+  box-orient: horizontal;
+  box-align: stretch;
+  /* Modern browsers */
+  display: flex;
+  flex-direction: row;
+  align-items: stretch;
+}
+div.unrecognized_cell .inner_cell {
+  border-radius: 4px;
+  padding: 5px;
+  font-weight: bold;
+  color: red;
+  border: 1px solid #cfcfcf;
+  background: #eaeaea;
+}
+@media (max-width: 480px) {
+  div.unrecognized_cell > div.prompt {
+    display: none;
+  }
+}
 /* any special styling for code cells that are currently running goes here */
 div.input {
   page-break-inside: avoid;
@@ -8757,6 +8787,12 @@ input.raw_input:focus {
 p.p-space {
   margin-bottom: 10px;
 }
+div.output_unrecognized {
+  border-radius: 4px;
+  padding: 5px;
+  font-weight: bold;
+  color: red;
+}
 .rendered_html {
   color: #000000;
   /* any extras will just be numbers: */