diff --git a/IPython/parallel/apps/baseapp.py b/IPython/parallel/apps/baseapp.py
index 9a4c24c..fa645fd 100644
--- a/IPython/parallel/apps/baseapp.py
+++ b/IPython/parallel/apps/baseapp.py
@@ -272,5 +272,5 @@ class BaseParallelApplication(BaseIPythonApplication):
                     " Making the likely assumption that it is."%pid
                 )
                 return True
-            pids = list(map(int, re.findall(r'^\W*\d+', output, re.MULTILINE)))
+            pids = list(map(int, re.findall(br'^\W*\d+', output, re.MULTILINE)))
             return pid in pids