diff --git a/plugins/knot/knot b/plugins/knot/knot
index d512adea..5d585c38 100755
--- a/plugins/knot/knot
+++ b/plugins/knot/knot
@@ -122,7 +122,7 @@ def get_stats():
 
     # After server reboot output can be almost empty. Use cached results
     # instead, needed for plugin config when using munin-async.
-    cachename = os.getenv('MUNIN_PLUGSTATE') + '/knot.state'
+    cachename = os.path.join(os.getenv('MUNIN_PLUGSTATE'), 'knot.state')
     if len(output) > 2048:
         with open(cachename, 'wt') as cache:
             cache.write(output)