diff --git a/summarize.py b/summarize.py
index a5b56fe..d8c3a4c 100644
--- a/summarize.py
+++ b/summarize.py
@@ -94,7 +94,11 @@ def _content_words(sentence):
     """
     words = []
     for raw in sentence.split():
-        token = _TOKEN_STRIP_RE.sub("", raw).lower()
+        # Optimization: bypass the heavy regex for strictly alphanumeric words
+        if raw.isalnum():
+            token = raw.lower()
+        else:
+            token = _TOKEN_STRIP_RE.sub("", raw).lower()
         if token and token not in _STOPWORDS:
             words.append(token)
     return words