--- a/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/FrameState.java	Fri Aug 17 11:56:59 2018 -0500
+++ b/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/FrameState.java	Fri Aug 17 13:20:53 2018 -0700
@@ -237,7 +237,8 @@
     }
 
     public void setOuterFrameState(FrameState x) {
-        assert x == null || (!x.isDeleted() && x.bci >= 0);
+        assert x == null || (!x.isDeleted() && x.bci >= 0) : "cannot set outer frame state of:\n" + toString(this) +
+                        "\nto:\n" + toString(x) + "\nisDeleted=" + x.isDeleted();
         updateUsages(this.outerFrameState, x);
         this.outerFrameState = x;
     }