diff --git a/run_mypy.py b/run_mypy.py
index 25ab54c0bf..88adea8db9 100644
--- a/run_mypy.py
+++ b/run_mypy.py
@@ -4,8 +4,7 @@ import sys
 import subprocess
 
 # A quick Python implementation of unix 'where' command.
-def where(exeName):
-    searchPath = os.getenv("PATH")
+def where(exeName, searchPath=os.getenv("PATH")):
     paths = searchPath.split(";" if sys.platform == "win32" else ":")
     for path in paths:
         candidatePath = os.path.join(path, exeName)
@@ -21,10 +20,18 @@ def findModules(path):
     return result
 
 def main():
+    # Find Uranium via the PYTHONPATH var
+    uraniumUMPath = where("UM", os.getenv("PYTHONPATH"))
+    if uraniumUMPath is None:
+        uraniumUMPath = os.path.join("..", "Uranium")
+    uraniumPath = os.path.dirname(uraniumUMPath)
+
+    mypyPathParts = [".", os.path.join(".", "plugins"), os.path.join(".", "plugins", "VersionUpgrade"),
+                     uraniumPath, os.path.join(uraniumPath, "stubs")]
     if sys.platform == "win32":
-        os.putenv("MYPYPATH", r".;.\plugins;.\plugins\VersionUpgrade;..\Uranium\;..\Uranium\stubs\\" )
+        os.putenv("MYPYPATH", ";".join(mypyPathParts))
     else:
-        os.putenv("MYPYPATH", r".:./plugins:./plugins/VersionUpgrade:../Uranium/:../Uranium\stubs/")
+        os.putenv("MYPYPATH", ":".join(mypyPathParts))
 
     # Mypy really needs to be run via its Python script otherwise it can't find its data files.
     mypyExe = where("mypy.bat" if sys.platform == "win32" else "mypy")