diff --git a/Lib/http/cookiejar.py b/Lib/http/cookiejar.py
index fb0fd2e9799..4ebb1601b4d 100644
--- a/Lib/http/cookiejar.py
+++ b/Lib/http/cookiejar.py
@@ -448,7 +448,7 @@ def join_header_words(lists):
         attr = []
         for k, v in pairs:
             if v is not None:
-                if not re.search(r"^\w+$", v):
+                if not v.isalnum() and '_' not in v:
                     v = HEADER_JOIN_ESCAPE_RE.sub(r"\\\1", v)  # escape " and \
                     v = '"%s"' % v
                 k = "%s=%s" % (k, v)
diff --git a/Misc/NEWS.d/next/Library/2025-01-18-11-40-11.gh-issue-128982.557lS5.rst b/Misc/NEWS.d/next/Library/2025-01-18-11-40-11.gh-issue-128982.557lS5.rst
new file mode 100644
index 00000000000..44b7a7b5373
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-01-18-11-40-11.gh-issue-128982.557lS5.rst
@@ -0,0 +1,2 @@
+Improve the performance of :func:`!http.cookiejar.join_header_words` by up
+to 35%. Patch by Bénédikt Tran.