1 files changed, 3 insertions, 1 deletions
diff --git a/Source/cmGeneratorExpressionDAGChecker.h b/Source/cmGeneratorExpressionDAGChecker.h
index 7e9c62a..a2e5ce4 100644
--- a/Source/cmGeneratorExpressionDAGChecker.h
+++ b/Source/cmGeneratorExpressionDAGChecker.h
@@ -28,7 +28,8 @@ struct cmGeneratorExpressionDAGChecker
   enum Result {
     DAG,
     SELF_REFERENCE,
-    CYCLIC_REFERENCE
+    CYCLIC_REFERENCE,
+    ALREADY_SEEN
   };
 
   Result check() const;
@@ -47,6 +48,7 @@ private:
   const cmGeneratorExpressionDAGChecker * const Parent;
   const std::string Target;
   const std::string Property;
+  std::map<cmStdString, std::set<cmStdString> > Seen;
   const GeneratorExpressionContent * const Content;
   const cmListFileBacktrace Backtrace;
   Result CheckResult;