--- a/Tools_BrowserList.st	Sat Feb 22 13:40:43 2014 +0100
+++ b/Tools_BrowserList.st	Sat Feb 22 13:42:00 2014 +0100
@@ -188,6 +188,8 @@
 environment:env
     | prevenv |
 
+    self assert:(env isNil or:[env isNameSpace or:[env == Smalltalk]]).
+
     prevenv := environment.
     environment := env.
     environment ~~ prevenv ifTrue:[
@@ -1890,10 +1892,10 @@
 !BrowserList class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libtool/Tools_BrowserList.st,v 1.60 2014-02-05 18:57:48 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libtool/Tools_BrowserList.st,v 1.61 2014-02-22 12:42:00 cg Exp $'
 !
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libtool/Tools_BrowserList.st,v 1.60 2014-02-05 18:57:48 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libtool/Tools_BrowserList.st,v 1.61 2014-02-22 12:42:00 cg Exp $'
 ! !