--- a/ProjectDefinition.st	Mon Dec 21 19:59:51 2009 +0100
+++ b/ProjectDefinition.st	Mon Dec 21 23:46:09 2009 +0100
@@ -4069,8 +4069,9 @@
                 |cls|
 
                 cls := (Smalltalk at:eachName asSymbol).
-                cls isNil ifTrue:[
-                    Transcript showCR:('ProjectDefinition: missing class: ', eachName).
+                (cls isNil or:[cls isBehavior not]) ifTrue:[
+                    Transcript showCR:('ProjectDefinition: missing/invalid class: ', eachName).
+                    cls := nil.
                 ].
                 cls.
             ]
@@ -4110,8 +4111,9 @@
                 |cls|
 
                 cls := (Smalltalk at:eachName asSymbol).
-                cls isNil ifTrue:[
-                    self warn:'Missing class: ',eachName.
+                cls isBehavior ifFalse:[
+                    self warn:'Missing/invalid class: ',eachName.
+                    cls := nil.
                 ].
                 cls
             ]
@@ -5291,11 +5293,11 @@
 !ProjectDefinition class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/ProjectDefinition.st,v 1.295 2009-12-17 19:50:36 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/ProjectDefinition.st,v 1.296 2009-12-21 22:46:09 cg Exp $'
 !
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libbasic/ProjectDefinition.st,v 1.295 2009-12-17 19:50:36 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/ProjectDefinition.st,v 1.296 2009-12-21 22:46:09 cg Exp $'
 ! !
 
 ProjectDefinition initialize!