diff --git a/overviewer.py b/overviewer.py
index 8a774f9..2a93845 100755
--- a/overviewer.py
+++ b/overviewer.py
@@ -304,6 +304,21 @@ dir but you forgot to put quotes around the directory, since it contains spaces.
         if render.get('forcerender', False):
             render['renderchecks'] = 2
 
+        # check if overlays are set, if so, make sure that those renders exist
+        if render.get('overlay', []) != []:
+            for x in render.get('overlay'):
+                if x != rname:
+                    try:
+                        renderLink = config['renders'][x]
+                    except KeyError:
+                        logging.error("Render %s's overlay is '%s', but I could not find a corresponding entry in the renders dictionary.",
+                                rname, x)
+                        return 1
+                    # TODO: Link the overlay rendering to the render modes it is used for so that the JS can properly fill in the dropdown
+                else:
+                    logging.error("Render %s's overlay contains itself.", rname)
+                    return 1
+
     destdir = config['outputdir']
     if not destdir:
         logging.error("You must specify the output directory in your config file.")
diff --git a/overviewer_core/settingsValidators.py b/overviewer_core/settingsValidators.py
index 7b023a8..227f4d3 100644
--- a/overviewer_core/settingsValidators.py
+++ b/overviewer_core/settingsValidators.py
@@ -55,7 +55,8 @@ def validateOverlays(renderlist):
     if type(renderlist) != list:
         raise ValidationException("Overlay must specify a list of renders")
     for x in renderlist:
-        print x
+        if validateStr(x) == '':
+            raise ValidationException("%r must be a string"% x)
     return renderlist
 
 def validateWorldPath(worldpath):