diff --git a/frappe/concurrency_limiter.py b/frappe/concurrency_limiter.py
index 0fe2e1a534..c75f0ad67f 100644
--- a/frappe/concurrency_limiter.py
+++ b/frappe/concurrency_limiter.py
@@ -56,7 +56,7 @@ def concurrent_limit(limit: int | None = None, wait_timeout: int | None = None):
 		def wrapper(*args, **kwargs):
 			# Skip concurrency limiting outside of HTTP requests (background jobs,
 			# CLI commands, tests that call functions directly, etc.).
-			if not getattr(frappe.local, "request", None):
+			if getattr(frappe.local, "request", None) is None:
 				return fn(*args, **kwargs)
 
 			effective_limit = int(limit) if limit is not None else _default_limit()
@@ -72,9 +72,11 @@ def concurrent_limit(limit: int | None = None, wait_timeout: int | None = None):
 			if not acquired:
 				from frappe.exceptions import ServiceUnavailableError
 
-				exc = ServiceUnavailableError(frappe._("Server is busy. Please try again in a few seconds."))
 				retry_after = max(1, int(effective_wait))
-				frappe.local.response_headers.set("Retry-After", str(retry_after))
+				if (headers := getattr(frappe.local, "response_headers", None)) is not None:
+					headers.set("Retry-After", str(retry_after))
+				exc = ServiceUnavailableError(frappe._("Server is busy. Please try again in a few seconds."))
+				exc.retry_after = retry_after
 				raise exc
 
 			try:
diff --git a/frappe/tests/test_concurrency_limiter.py b/frappe/tests/test_concurrency_limiter.py
index 67755c2db5..9f4818cd24 100644
--- a/frappe/tests/test_concurrency_limiter.py
+++ b/frappe/tests/test_concurrency_limiter.py
@@ -10,8 +10,12 @@ from frappe.exceptions import ServiceUnavailableError
 from frappe.tests import IntegrationTestCase
 
 
+def _cache_name(fn):
+	return f"concurrency:{fn.__module__}.{fn.__qualname__}"
+
+
 def _cache_key(fn):
-	return frappe.cache.make_key(f"concurrency:{fn.__module__}.{fn.__qualname__}")
+	return frappe.cache.make_key(_cache_name(fn))
 
 
 class TestConcurrentLimit(IntegrationTestCase):
@@ -37,7 +41,7 @@ class TestConcurrentLimit(IntegrationTestCase):
 
 		self.assertEqual(calls, [True])
 		# Counter must not have been touched
-		self.assertIsNone(frappe.cache.get(_cache_key(fn)))
+		self.assertFalse(frappe.cache.exists(_cache_key(fn)))
 
 	def test_raises_immediately_when_limit_full(self):
 		"""ServiceUnavailableError is raised at once when wait_timeout=0 and the
@@ -69,7 +73,7 @@ class TestConcurrentLimit(IntegrationTestCase):
 		try:
 			frappe.local.request = frappe._dict()
 			fn()
-			self.assertEqual(int(frappe.cache.get(key) or 0), 0)
+			self.assertEqual(frappe.cache.incrby(_cache_key(fn), 0), 0)
 		finally:
 			del frappe.local.request
 			frappe.cache.delete(key)
@@ -86,7 +90,7 @@ class TestConcurrentLimit(IntegrationTestCase):
 		try:
 			frappe.local.request = frappe._dict()
 			self.assertRaises(ValueError, fn)
-			self.assertEqual(int(frappe.cache.get(key) or 0), 0)
+			self.assertEqual(frappe.cache.incrby(_cache_key(fn), 0), 0)
 		finally:
 			del frappe.local.request
 			frappe.cache.delete(key)
@@ -149,7 +153,7 @@ class TestConcurrentLimit(IntegrationTestCase):
 		_release(key)  # correct release → 0
 		_release(key)  # spurious extra release
 
-		counter = int(frappe.cache.get(key) or 0)
+		counter = frappe.cache.incrby(key, 0)
 		frappe.cache.delete(key)
 
 		self.assertGreaterEqual(counter, 0)