diff --git a/platform/core-impl/src/com/intellij/openapi/editor/impl/IntervalTreeImpl.java b/platform/core-impl/src/com/intellij/openapi/editor/impl/IntervalTreeImpl.java
index e6e302947bc4..e70292090890 100644
--- a/platform/core-impl/src/com/intellij/openapi/editor/impl/IntervalTreeImpl.java
+++ b/platform/core-impl/src/com/intellij/openapi/editor/impl/IntervalTreeImpl.java
@@ -137,7 +137,7 @@ public abstract class IntervalTreeImpl<T extends MutableInterval> extends RedBla
           return false;
         }
       }
-      assert false: "interval not found: "+key +"; "+ intervals;
+      assert false: "interval not found: "+key +"; "+ intervals+"; isValid="+key.isValid();
       return false;
     }