--- a/ProjectDefinition.st	Mon Mar 11 11:59:49 2019 +0100
+++ b/ProjectDefinition.st	Tue Mar 12 15:36:20 2019 +0100
@@ -8139,12 +8139,26 @@
 !
 
 reasonForNotSupportedOnPlatform
-    "answer a reason string, why the package is not supported on this platform
-     (if it is not, i.e. if supportedByPlatform returns false)"
-
-    ^ 'not supported by this OS-platform'
+    "answer false, if this package is not suitable for
+     the current platform. The default here returns true.
+     Only to be redefined in packages which are definitely not valid
+     for the given platform. For example, the OLE package is only
+     usable under windows"
+
+    self preRequisites do:[:eachProjectDefinitionClassNameSymbol|
+        |cls|
+        cls := self definitionClassForPackage:eachProjectDefinitionClassNameSymbol.
+        cls isNil ifTrue:[
+            ^ 'Prerequisite package "', eachProjectDefinitionClassNameSymbol, '" is missing'.
+        ].
+        cls supportedOnPlatform ifFalse:[
+            ^ 'Prerequisite package "', eachProjectDefinitionClassNameSymbol, '" is not supported: ', cls reasonForNotSupportedOnPlatform.
+        ].
+    ].
+    ^ ''.
 
     "Created: / 07-02-2019 / 14:21:54 / Claus Gittinger"
+    "Modified: / 12-03-2019 / 15:26:07 / Stefan Vogel"
 !
 
 supportedOnPlatform
@@ -8154,7 +8168,19 @@
      for the given platform. For example, the OLE package is only
      usable under windows"
 
-    ^ true
+    self preRequisites do:[:eachProjectDefinitionClassNameSymbol|
+        |cls|
+        cls := self definitionClassForPackage:eachProjectDefinitionClassNameSymbol.
+        cls isNil ifTrue:[
+            ^ false.    "prerequisite project is missing"
+        ].
+        cls supportedOnPlatform ifFalse:[
+            ^ false.
+        ].
+    ].
+    ^ true.
+
+    "Modified: / 12-03-2019 / 15:26:00 / Stefan Vogel"
 !
 
 whoReferences:aPackageString