--- a/install.py	Wed Mar 22 18:45:15 2017 +0100
+++ b/install.py	Wed Mar 22 18:50:20 2017 +0100
@@ -425,7 +425,7 @@
     return wname
 
 
-def copyTree(src, dst, filters, excludeDirs=[], excludePatterns=[]):
+def copyTree(src, dst, filters, excludeDirs=None, excludePatterns=None):
     """
     Copy Python, translation, documentation, wizards configuration,
     designer template files and DTDs of a directory tree.
@@ -437,6 +437,10 @@
     @keyparam excludePatterns list of filter pattern determining the files to
         be skipped
     """
+    if excludeDirs is None:
+        excludeDirs = []
+    if excludePatterns is None:
+        excludePatterns = []
     try:
         names = os.listdir(src)
     except OSError: