diff --git a/net/test/tcp_fastopen_test.py b/net/test/tcp_fastopen_test.py
index 5b89a2d..9c777c6 100755
--- a/net/test/tcp_fastopen_test.py
+++ b/net/test/tcp_fastopen_test.py
@@ -22,6 +22,7 @@
 
 import multinetwork_base
 import net_test
+import os
 import packets
 import tcp_metrics
 
@@ -67,6 +68,9 @@
   def clearBlackhole(self):
     if net_test.LINUX_VERSION < (4, 14, 0):
       return
+    # Prior to 4.15 this sysctl is not namespace aware.
+    if net_test.LINUX_VERSION < (4, 15, 0) and not os.path.exists(BH_TIMEOUT_SYSCTL):
+      return
     timeout = self.GetSysctl(BH_TIMEOUT_SYSCTL)
 
     # Write to timeout to clear any pre-existing blackhole condition