1 files changed, 2 insertions, 0 deletions
diff --git a/Source/AbsInt/LoopInvariantsOnDemand.cs b/Source/AbsInt/LoopInvariantsOnDemand.cs
index 49958289..5bb5916d 100644
--- a/Source/AbsInt/LoopInvariantsOnDemand.cs
+++ b/Source/AbsInt/LoopInvariantsOnDemand.cs
@@ -55,6 +55,8 @@ namespace Microsoft.Boogie.AbstractInterpretation {
         return VisitFunApp((AI.IFunApp)expr);
       else if (expr is AI.IFunction)
         return VisitFunction((AI.IFunction)expr);
+      else if (expr is AI.IUnknown)
+        return null;
       else {
         Contract.Assert(false);
         throw new cce.UnreachableException();