diff --git a/src/FAST-Core-Tools/FASTDifferentialValidator.class.st b/src/FAST-Core-Tools/FASTDifferentialValidator.class.st
index 9719c19..4ee6a8b 100644
--- a/src/FAST-Core-Tools/FASTDifferentialValidator.class.st
+++ b/src/FAST-Core-Tools/FASTDifferentialValidator.class.st
@@ -84,7 +84,7 @@ FASTDifferentialValidator >> getASTFromFileReference: aFileReference [
 
 	| model |
 	aFileReference readStreamDo: [ :stream |
-		model := self getASTFromString: stream ].
+		model := self getASTFromString: stream contents ].
 
 	^self getTopLevelNodes: model
 ]