--- a/Utilities/__init__.py	Thu Oct 29 19:10:20 2015 +0100
+++ b/Utilities/__init__.py	Fri Oct 30 18:18:48 2015 +0100
@@ -632,7 +632,11 @@
             flags[key] = value
         else:
             # treat it as a boolean
-            flags[flag] = True
+            if flag[0] == "-":
+                # false flags start with '-'
+                flags[flag[1:]] = False
+            else:
+                flags[flag] = True
     
     return flags