diff --git a/t/lib-httpd/http-429.sh b/t/lib-httpd/http-429.sh
index c97b16145b..904cdacbd0 100644
--- a/t/lib-httpd/http-429.sh
+++ b/t/lib-httpd/http-429.sh
@@ -3,7 +3,7 @@
 # Script to return HTTP 429 Too Many Requests responses for testing retry logic.
 # Usage: /http_429/<test-context>/<retry-after-value>/<repo-path>
 #
-# The test-context is a unique identifier for each test to isolate state files.
+# The test-context is a unique identifier for each test to isolate state directories.
 # The retry-after-value can be:
 #   - A number (e.g., "1", "2", "100") - sets Retry-After header to that many seconds
 #   - "none" - no Retry-After header
@@ -26,14 +26,24 @@ repo_path="${remaining#*/}"  # Get rest (repo path)
 # The repo name is the first component before any "/"
 repo_name="${repo_path%%/*}"
 
-# Use current directory (HTTPD_ROOT_PATH) for state file
-# Create a safe filename from test_context, retry_after and repo_name
-# This ensures all requests for the same test context share the same state file
+# Store state in the current directory (HTTPD_ROOT_PATH). Build a safe name
+# from test_context, retry_after, and repo_name, so that all requests for one
+# test context share the same state.
 safe_name=$(echo "${test_context}-${retry_after}-${repo_name}" | tr '/' '_' | tr -cd 'a-zA-Z0-9_-')
-state_file="http-429-state-${safe_name}"
+state="http-429-state-${safe_name}"
 
-# Check if this is the first call (no state file exists)
-if test -f "$state_file"
+# This endpoint returns 429 to the first request. It forwards every later
+# request to git-http-backend, so the retry succeeds. Apache can run this CGI
+# for several requests at the same time. A single atomic "mkdir" selects the
+# first request, because only one "mkdir" succeeds. That request returns 429
+# and leaves the directory as the "already rate-limited" marker. Every later
+# "mkdir" fails, so the endpoint forwards those requests.
+#
+# "permanent" is the exception. It must return 429 to every request, so it
+# skips the "mkdir" and records no state. A leftover directory would let a
+# later "permanent" request find the marker. The endpoint would forward that
+# request, which "permanent" must not allow.
+if test "$retry_after" != permanent && ! mkdir "$state" 2>/dev/null
 then
 	# Already returned 429 once, forward to git-http-backend
 	# Set PATH_INFO to just the repo path (without retry-after value)
@@ -52,9 +62,6 @@ then
 	exec "$GIT_EXEC_PATH/git-http-backend"
 fi
 
-# Mark that we've returned 429
-touch "$state_file"
-
 # Output HTTP 429 response
 printf "Status: 429 Too Many Requests\r\n"
 
@@ -67,8 +74,7 @@ case "$retry_after" in
 		printf "Retry-After: invalid-format-123abc\r\n"
 		;;
 	permanent)
-		# Always return 429, don't set state file for success
-		rm -f "$state_file"
+		# Always return 429
 		printf "Retry-After: 1\r\n"
 		printf "Content-Type: text/plain\r\n"
 		printf "\r\n"