diff --git a/idea/idea-analysis/src/org/jetbrains/kotlin/idea/framework/JsLibraryStdDetectionUtil.java b/idea/idea-analysis/src/org/jetbrains/kotlin/idea/framework/JsLibraryStdDetectionUtil.java
index 434b06a15c0..d8f1c48a754 100644
--- a/idea/idea-analysis/src/org/jetbrains/kotlin/idea/framework/JsLibraryStdDetectionUtil.java
+++ b/idea/idea-analysis/src/org/jetbrains/kotlin/idea/framework/JsLibraryStdDetectionUtil.java
@@ -63,7 +63,7 @@ public class JsLibraryStdDetectionUtil {
             if (root.getFileSystem().getProtocol() != StandardFileSystems.JAR_PROTOCOL) continue;
 
             VirtualFile jar = VfsUtilCore.getVirtualFileForJar(root);
-            assert jar != null;
+            assert jar != null : "expected not null for root '" + root.getPath() + "'";
 
             if (LibraryUtils.isKotlinJavascriptStdLibrary(new File(jar.getPath()))) {
                 return jar;