--- a/testing/mozbase/mozprocess/mozprocess/processhandler.py
+++ b/testing/mozbase/mozprocess/mozprocess/processhandler.py
@@ -197,24 +197,40 @@ class ProcessHandlerMixin(object):
                     # a signal was explicitly set or not posix
                     send_sig(sig or signal.SIGKILL)
 
             self.returncode = self.wait()
             self._cleanup()
             return self.returncode
 
         def poll(self):
-            """ Popen.poll
-                Check if child process has terminated. Set and return returncode attribute.
+            """Check if child process has terminated, and set returncode attribute.
+
+            This method overrides the Popen.poll implementation for our custom
+            process handling for Windows.
             """
-            # If we have a handle, the process is alive
-            if isWin and getattr(self, '_handle', None):
-                return None
+            if isWin:
+                if self._handle:
+                    returncode = winprocess.GetExitCodeProcess(self._handle)
 
-            return subprocess.Popen.poll(self)
+                    # If the process doesn't exist anymore run cleanup steps
+                    if returncode != winprocess.STILL_ACTIVE:
+                        self.returncode = returncode
+                        self._cleanup()
+                    else:
+                        self.returncode = None
+
+                else:
+                    # Dude, the process is like totally dead!
+                    return self.returncode
+
+            else:
+                self.returncode = subprocess.Popen.poll(self)
+
+            return self.returncode
 
         def wait(self):
             """ Popen.wait
                 Called to wait for a running process to shut down and return
                 its exit code
                 Returns the main process's exit code
             """
             # This call will be different for each OS