diff --git a/platform/platform-impl/src/com/intellij/openapi/diff/impl/external/CompositeDiffTool.java b/platform/platform-impl/src/com/intellij/openapi/diff/impl/external/CompositeDiffTool.java
index 58b430f4247f..851a9d06b290 100644
--- a/platform/platform-impl/src/com/intellij/openapi/diff/impl/external/CompositeDiffTool.java
+++ b/platform/platform-impl/src/com/intellij/openapi/diff/impl/external/CompositeDiffTool.java
@@ -56,7 +56,7 @@ class CompositeDiffTool implements DiffTool {
   private static void checkDiffData(@NotNull DiffRequest data) {
     DiffContent[] contents = data.getContents();
     for (DiffContent content : contents) {
-      LOG.assertTrue(content != null);
+      LOG.assertTrue(content != null, "Null content in diff request");
     }
   }
 }