diff --git a/cura/LayerPolygon.py b/cura/LayerPolygon.py
index 70b17cff75..81fe66a80d 100644
--- a/cura/LayerPolygon.py
+++ b/cura/LayerPolygon.py
@@ -1,6 +1,6 @@
 from UM.Math.Color import Color
 from UM.Application import Application
-
+from typing import Any
 import numpy
 
 
@@ -173,7 +173,7 @@ class LayerPolygon:
 
         return normals
 
-    __color_map = None
+    __color_map = None # type: numpy.ndarray[Any]
 
     ##  Gets the instance of the VersionUpgradeManager, or creates one.
     @classmethod
diff --git a/run_mypy.py b/run_mypy.py
index c5dfb23802..24c9d3ae31 100644
--- a/run_mypy.py
+++ b/run_mypy.py
@@ -1,8 +1,17 @@
 #!env python
 import os
+import sys
 import subprocess
 
-os.putenv("MYPYPATH", r".;.\plugins;.\plugins\VersionUpgrade;..\Uranium_hint\;..\Uranium_hint\stubs\\" )
+# A quick Python implementation of unix 'where' command.
+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)
+        if os.path.exists(candidatePath):
+            return candidatePath
+    return None
 
 def findModules(path):
     result = []
@@ -11,21 +20,30 @@ def findModules(path):
             result.append(entry.name)
     return result
 
-plugins = findModules("plugins")
-plugins.sort()
+def main():
+    os.putenv("MYPYPATH", r".;.\plugins;.\plugins\VersionUpgrade;..\Uranium_hint\;..\Uranium_hint\stubs\\" )
 
-mods = ["cura"] + plugins + findModules("plugins/VersionUpgrade")
+    # 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")
+    mypyModule = os.path.join(os.path.dirname(mypyExe), "mypy")
 
-for mod in mods:
-    print("------------- Checking module {mod}".format(**locals()))
-    result = subprocess.run(["python", r"c:\python35\Scripts\mypy", "-p", mod])
-    if result.returncode != 0:
+    plugins = findModules("plugins")
+    plugins.sort()
+
+    mods = ["cura"] + plugins + findModules("plugins/VersionUpgrade")
+
+    for mod in mods:
+        print("------------- Checking module {mod}".format(**locals()))
+        result = subprocess.run([sys.executable, mypyModule, "-p", mod])
+        if result.returncode != 0:
+            print("""
+    Module {mod} failed checking. :(
+    """.format(**locals()))
+            break
+    else:
         print("""
-Module {mod} failed checking. :(
-""".format(**locals()))
-        break
-else:
-    print("""
 
-Done checking. All is good.
-""")
+    Done checking. All is good.
+    """)
+    return 0
+sys.exit(main())