diff --git a/Lib/urlparse.py b/Lib/urlparse.py
index 6261b24..99ebe6a 100644
--- a/Lib/urlparse.py
+++ b/Lib/urlparse.py
@@ -187,11 +187,12 @@
             v = SplitResult(scheme, netloc, url, query, fragment)
             _parse_cache[key] = v
             return v
-        for c in url[:i]:
-            if c not in scheme_chars:
-                break
-        else:
-            scheme, url = url[:i].lower(), url[i+1:]
+        if url.endswith(':') or not url[i+1].isdigit():
+            for c in url[:i]:
+                if c not in scheme_chars:
+                    break
+            else:
+                scheme, url = url[:i].lower(), url[i+1:]
 
     if url[:2] == '//':
         netloc, url = _splitnetloc(url, 2)