--- a/testing/mozharness/mozharness/base/python.py
+++ b/testing/mozharness/mozharness/base/python.py
@@ -507,22 +507,28 @@ class ResourceMonitoringMixin(object):
     While we would like to record resource usage for the entirety of a script,
     since we require an external package, we can only record resource usage
     after that package is installed (as part of creating the virtualenv).
     That's just the way things have to be.
     """
     def __init__(self, *args, **kwargs):
         super(ResourceMonitoringMixin, self).__init__(*args, **kwargs)
 
-        self.register_virtualenv_module('psutil>=3.1.1', method='pip',
+        if self.topsrcdir:
+            psutil = os.path.join(self.topsrcdir, 'python', 'psutil')
+            mozsystemmonitor = os.path.join(self.topsrcdir, 'testing',
+                                            'mozbase', 'mozsystemmonitor')
+        else:
+            psutil = 'psutil>=3.1.1'
+            mozsystemmonitor = 'mozsystemmonitor==0.3'
+
+        self.register_virtualenv_module(psutil, method='pip', optional=True)
+        self.register_virtualenv_module(mozsystemmonitor, method='pip',
                                         optional=True)
-        self.register_virtualenv_module('mozsystemmonitor==0.3',
-                                        method='pip', optional=True)
-        self.register_virtualenv_module('jsonschema==2.5.1',
-                                        method='pip')
+        self.register_virtualenv_module('jsonschema==2.5.1', method='pip')
         # explicitly install functools32, because some slaves aren't using
         # a version of pip recent enough to install it automatically with
         # jsonschema (which depends on it)
         # https://github.com/Julian/jsonschema/issues/233
         self.register_virtualenv_module('functools32==3.2.3-2',
                                         method='pip')
         self._resource_monitor = None