1 files changed, 5 insertions, 1 deletions
diff --git a/markdown/util.py b/markdown/util.py
index fa50e83..9ae523f 100644
--- a/markdown/util.py
+++ b/markdown/util.py
@@ -51,9 +51,13 @@ AUXILIARY GLOBAL FUNCTIONS
 
 def isBlockLevel(tag):
     """Check if the tag is a block level HTML tag."""
+    if isinstance(tag, basestring):
+        return BLOCK_LEVEL_ELEMENTS.match(tag)
+    # Some ElementTree tags are not strings, so return True for Comments
+    # and False for anything else.
     if tag is etree.Comment:
         return True
-    return BLOCK_LEVEL_ELEMENTS.match(tag)
+    return False
 
 """
 MISC AUXILIARY CLASSES