diff --git a/IPython/utils/_process_posix.py b/IPython/utils/_process_posix.py
index d6d53ef..9c6054f 100644
--- a/IPython/utils/_process_posix.py
+++ b/IPython/utils/_process_posix.py
@@ -187,7 +187,16 @@ class ProcessHandler(object):
 
         # We follow the subprocess pattern, returning either the exit status
         # as a positive number, or the terminating signal as a negative
-        # number. sh returns 128+n for signals
+        # number.
+        # on Linux, sh returns 128+n for signals terminating child processes on Linux
+        # on BSD (OS X), the signal code is set instead
+        if child.exitstatus is None:
+            # on WIFSIGNALED, pexpect sets signalstatus, leaving exitstatus=None
+            if child.signalstatus is None:
+                # this condition may never occur,
+                # but let's be certain we always return an integer.
+                return 0
+            return -child.signalstatus
         if child.exitstatus > 128:
             return -(child.exitstatus - 128)
         return child.exitstatus