diff --git a/css/main.css b/css/main.css
index 70c8eb7330cfeff45b611040768827d9f55b3572..592d40811f645cd06d6500e873e0a61c2ba6c174 100644
--- a/css/main.css
+++ b/css/main.css
@@ -211,7 +211,7 @@ hr {
 
 .inlineWarning {
     background-color: rgba(255,0,0,0.15);
-    padding: 10px 15px 15px 15px;
+    padding: 15px;
     margin: 0 0 20px 0;
 }
 
diff --git a/js/cam/cam.js b/js/cam/cam.js
index 618afded94a8e3c003a5204eff4e74f4b0456cd1..910934e3f768dfdb2e92a770705d504fdd0f7116 100644
--- a/js/cam/cam.js
+++ b/js/cam/cam.js
@@ -91,7 +91,7 @@ define(['underscore', 'three', 'backbone', 'appState', 'latticeCAM', 'threeModel
 
 
         _calculateNumMaterials: function(){//todo calc length of gik cells as separate material types
-            this.set("allCAMMaterialTypes", materials.getChildCellTypes(lattice.sparseCells, true));
+            this.set("allCAMMaterialTypes", materials.getChildCellTypes(lattice.sparseCells, true) || []);
         },
 
 
diff --git a/js/menus/templates/AssemblerMenuView.html b/js/menus/templates/AssemblerMenuView.html
index 067ad9f3c711deaef722069ec6fc95b2b594b0a5..38ca20d02edf01a45ccc1185021b698c9228a8bf 100644
--- a/js/menus/templates/AssemblerMenuView.html
+++ b/js/menus/templates/AssemblerMenuView.html
@@ -1,3 +1,6 @@
+<% if (numCells == 0){ %>
+    <div class="inlineWarning">No cells in assembly!</div>
+<% } %>
 Machine: &nbsp;&nbsp;
     <div class="btn-group">
         <button data-toggle="dropdown" class="btn dropdown-toggle" type="button"><%= allMachines[machineName].name %><span class="caret"></span></button>