diff --git a/tools/run_tests/python_utils/port_server.py b/tools/run_tests/python_utils/port_server.py
index 4fb5ca0e94b..e8ac71af8d7 100755
--- a/tools/run_tests/python_utils/port_server.py
+++ b/tools/run_tests/python_utils/port_server.py
@@ -57,6 +57,17 @@ pool = []
 in_use = {}
 mu = threading.Lock()
 
+# Cronet restricts the following ports to be used (see
+# https://cs.chromium.org/chromium/src/net/base/port_util.cc). When one of these
+# ports is used in a Cronet test, the test would fail (see issue #12149). These
+# ports must be excluded from pool.
+cronet_restricted_ports = [1, 7, 9, 11, 13, 15, 17, 19, 20, 21, 22, 23, 25, 37,
+                           42, 43, 53, 77, 79, 87, 95, 101, 102, 103, 104, 109,
+                           110, 111, 113, 115, 117, 119, 123, 135, 139, 143,
+                           179, 389, 465, 512, 513, 514, 515, 526, 530, 531,
+                           532, 540, 556, 563, 587, 601, 636, 993, 995, 2049,
+                           3659, 4045, 6000, 6665, 6666, 6667, 6668, 6669, 6697]
+
 def can_connect(port):
   # this test is only really useful on unices where SO_REUSE_PORT is available
   # so on Windows, where this test is expensive, skip it
@@ -84,7 +95,7 @@ def can_bind(port, proto):
 
 def refill_pool(max_timeout, req):
   """Scan for ports not marked for being in use"""
-  chk = list(range(1025, 32766))
+  chk = [port for port in list(range(1025, 32766)) if port not in cronet_restricted_ports]
   random.shuffle(chk)
   for i in chk:
     if len(pool) > 100: break