--- a/ClassBuilder.st	Tue Sep 25 10:35:22 2018 +0200
+++ b/ClassBuilder.st	Tue Sep 25 12:25:08 2018 +0200
@@ -1,5 +1,3 @@
-"{ Encoding: utf8 }"
-
 "
  COPYRIGHT (c) 2001 by eXept Software AG
               All Rights Reserved
@@ -235,34 +233,40 @@
 
     methodDict keysAndValuesDo:[:selector :method |
         oldMethod := method originalMethodIfWrapped.
-
-        "before parsing (which may take some time),
-         do a string search if it's only one variable,
-         we are looking for.
-         Could look for more than one variable by string compare, but then
-         parsing it right away may be faster ..."
-
-        source := oldMethod source.
-        ((nNames == 1) and:[superBoolean not]) ifTrue:[
-            mustInvalidate := (source findString:(setOfNames first)) ~~ 0.
-        ] ifFalse:[
-            ((nNames == 0) and:[superBoolean]) ifTrue:[
-                mustInvalidate := (source findString:'super') ~~ 0.
+        mustInvalidate := false.
+
+        "if we have no source, assume (hope) that the method is still valid.
+         When patching deployed systems without source, we
+         add instvar only to final classes at the end, so existing methods
+         should still be valid."
+        source notNil ifTrue:[
+            "before parsing (which may take some time),
+             do a string search if it's only one variable,
+             we are looking for.
+             Could look for more than one variable by string compare, but then
+             parsing it right away may be faster ..."
+
+            source := oldMethod source.
+            ((nNames == 1) and:[superBoolean not]) ifTrue:[
+                mustInvalidate := (source findString:(setOfNames first)) ~~ 0.
             ] ifFalse:[
-                mustInvalidate := true
+                ((nNames == 0) and:[superBoolean]) ifTrue:[
+                    mustInvalidate := (source findString:'super') ~~ 0.
+                ] ifFalse:[
+                    mustInvalidate := true
+                ].
+            ].
+
+            mustInvalidate ifTrue:[
+                "we have to parse it ..."
+                p := newClass parserClass parseMethod:source in:newClass.
+                (p isNil 
+                 or:[(p usedVars includesAny:setOfNames)
+                 or:[superBoolean and:[p usesSuper]]]) ifFalse:[
+                    mustInvalidate := false
+                ]
             ].
         ].
-
-        mustInvalidate ifTrue:[
-            "we have to parse it ..."
-            p := newClass parserClass parseMethod:source in:newClass.
-            (p isNil 
-             or:[(p usedVars includesAny:setOfNames)
-             or:[superBoolean and:[p usesSuper]]]) ifFalse:[
-                mustInvalidate := false
-            ]
-        ].
-
         mustInvalidate ifTrue:[
             newMethod := oldMethod copy.
 "/            Smalltalk silentLoading ifFalse:[