diff --git a/examples/simpleperf.py b/examples/simpleperf.py
index 53bf4bb..7ea269c 100755
--- a/examples/simpleperf.py
+++ b/examples/simpleperf.py
@@ -21,7 +21,7 @@ from sys import argv
 
 class SingleSwitchTopo(Topo):
     "Single switch connected to n hosts."
-    def build(self, n=2, lossy=True )
+    def build(self, n=2, lossy=True ):
         switch = self.addSwitch('s1')
         for h in range(n):
             # Each host gets 50%/n of system CPU