diff --git a/src/registry.py b/src/registry.py
index 21671a86d..3f7675909 100644
--- a/src/registry.py
+++ b/src/registry.py
@@ -327,16 +327,14 @@ class Value(Group):
 class Boolean(Value):
     """Value must be either True or False (or On or Off)."""
     def set(self, s):
-        s = s.strip().lower()
-        if s in ('true', 'on', 'enable', 'enabled'):
-            value = True
-        elif s in ('false', 'off', 'disable', 'disabled'):
-            value = False
-        elif s == 'toggle':
-            value = not self.value
-        else:
-            self.error()
-        self.setValue(value)
+        try:
+            v = utils.toBool(s)
+        except ValueError:
+            if s.strip().lower() == 'toggle':
+                v = not self.value
+            else:
+                self.error()
+        self.setValue(v)
 
     def setValue(self, v):
         super(Boolean, self).setValue(bool(v))
diff --git a/src/utils.py b/src/utils.py
index 021d796dc..c171ea5f6 100755
--- a/src/utils.py
+++ b/src/utils.py
@@ -807,21 +807,15 @@ def callTracer(fd=None, basename=True):
     return tracer
 
 
-# These are used by Owner and Misc for their callBefore/callAfter attributes.
-class Everything(object):
-    def __contains__(self, x):
+def toBool(s):
+    s = s.strip().lower()
+    if s in ('true', 'on', 'enable', 'enabled'):
         return True
-
-    def __iter__(self):
-        return iter([])
-
-class Nothing(object):
-    def __contains__(self, x):
+    elif s in ('false', 'off', 'disable', 'disabled'):
         return False
+    else:
+        raise ValueError, 'Invalid string for toBool: %r' % s
     
-    def __iter__(self):
-        return iter([])
-
 if __name__ == '__main__':
     import doctest
     doctest.testmod(sys.modules['__main__'])