diff --git a/testing/mozbase/mozprocess/mozprocess/processhandler.py b/testing/mozbase/mozprocess/mozprocess/processhandler.py
index a6d2befa12d..8268e67208d 100644
--- a/testing/mozbase/mozprocess/mozprocess/processhandler.py
+++ b/testing/mozbase/mozprocess/mozprocess/processhandler.py
@@ -65,6 +65,7 @@ class ProcessHandlerMixin(object):
 
         MAX_IOCOMPLETION_PORT_NOTIFICATION_DELAY = 180
         MAX_PROCESS_KILL_DELAY = 30
+        TIMEOUT_BEFORE_SIGKILL = 1.0
 
         def __init__(self,
                      args,
@@ -144,16 +145,32 @@ class ProcessHandlerMixin(object):
                     if err is not None:
                         raise OSError(err)
             else:
-                sig = sig or signal.SIGKILL
-                if not self._ignore_children:
-                    try:
-                        os.killpg(self.pid, sig)
-                    except BaseException, e:
-                        if getattr(e, "errno", None) != 3:
-                            # Error 3 is "no such process", which is ok
-                            print >> sys.stdout, "Could not kill process, could not find pid: %s, assuming it's already dead" % self.pid
+                def send_sig(sig):
+                    if not self._ignore_children:
+                        try:
+                            os.killpg(self.pid, sig)
+                        except BaseException, e:
+                            if getattr(e, "errno", None) != 3:
+                                # Error 3 is "no such process", which is ok
+                                print >> sys.stdout, "Could not kill process, could not find pid: %s, assuming it's already dead" % self.pid
+                    else:
+                        os.kill(self.pid, sig)
+
+                if sig is None and isPosix:
+                    # ask the process for termination and wait a bit
+                    send_sig(signal.SIGTERM)
+                    limit = time.time() + self.TIMEOUT_BEFORE_SIGKILL
+                    while time.time() <= limit:
+                        if self.poll() is not None:
+                            # process terminated nicely
+                            break
+                        time.sleep(0.02)
+                    else:
+                        # process did not terminate - send SIGKILL to force
+                        send_sig(signal.SIGKILL)
                 else:
-                    os.kill(self.pid, sig)
+                    # a signal was explicitly set or not posix
+                    send_sig(sig or signal.SIGKILL)
 
             self.returncode = self.wait()
             self._cleanup()
diff --git a/testing/mozbase/mozprocess/tests/infinite_loop.py b/testing/mozbase/mozprocess/tests/infinite_loop.py
new file mode 100644
index 00000000000..e38e425e054
--- /dev/null
+++ b/testing/mozbase/mozprocess/tests/infinite_loop.py
@@ -0,0 +1,18 @@
+import threading
+import time
+import sys
+import signal
+
+if 'deadlock' in sys.argv:
+    lock = threading.Lock()
+
+    def trap(sig, frame):
+        lock.acquire()
+
+    # get the lock once
+    lock.acquire()
+    # and take it again on SIGTERM signal: deadlock.
+    signal.signal(signal.SIGTERM, trap)
+
+while 1:
+    time.sleep(1)
diff --git a/testing/mozbase/mozprocess/tests/test_mozprocess_kill.py b/testing/mozbase/mozprocess/tests/test_mozprocess_kill.py
index 19859f4a989..08261951d60 100644
--- a/testing/mozbase/mozprocess/tests/test_mozprocess_kill.py
+++ b/testing/mozbase/mozprocess/tests/test_mozprocess_kill.py
@@ -4,6 +4,7 @@ import os
 import time
 import unittest
 import proctest
+import signal
 from mozprocess import processhandler
 
 here = os.path.dirname(os.path.abspath(__file__))
@@ -80,5 +81,26 @@ class ProcTestKill(proctest.ProcTest):
                               p.didTimeout,
                               expectedfail=('returncode',))
 
+    @unittest.skipUnless(processhandler.isPosix, "posix only")
+    def test_process_kill_with_sigterm(self):
+        script = os.path.join(here, 'infinite_loop.py')
+        p = processhandler.ProcessHandler([self.python, script])
+
+        p.run()
+        p.kill()
+
+        self.assertEquals(p.proc.returncode, -signal.SIGTERM)
+
+    @unittest.skipUnless(processhandler.isPosix, "posix only")
+    def test_process_kill_with_sigint_if_needed(self):
+        script = os.path.join(here, 'infinite_loop.py')
+        p = processhandler.ProcessHandler([self.python, script, 'deadlock'])
+
+        p.run()
+        time.sleep(1)
+        p.kill()
+
+        self.assertEquals(p.proc.returncode, -signal.SIGKILL)
+
 if __name__ == '__main__':
     unittest.main()