diff -r -u markdown/__init__.py markdown_/__init__.py
--- markdown/__init__.py	2009-03-30 06:31:40.000000000 +0000
+++ markdown_/__init__.py	2009-04-21 20:30:32.000000000 +0000
@@ -397,9 +397,11 @@
         # Serialize _properly_.  Strip top-level tags.
         output, length = codecs.utf_8_decode(self.serializer(root, encoding="utf8"))
         if self.stripTopLevelTags:
-            start = output.index('<%s>'%DOC_TAG)+len(DOC_TAG)+2
-            end = output.rindex('</%s>'%DOC_TAG)
-            output = output[start:end].strip()
+            start = output.find('<%s>'%DOC_TAG)
+            if start != -1:
+                start = start+len(DOC_TAG)+2
+                end = output.rindex('</%s>'%DOC_TAG)
+                output = output[start:end].strip()
 
         # Run the text post-processors
         for pp in self.postprocessors.values():