diff --git a/idea/src/org/jetbrains/jet/plugin/JetPluginUtil.java b/idea/src/org/jetbrains/jet/plugin/JetPluginUtil.java
index 5ec69cce831..c469efb2990 100644
--- a/idea/src/org/jetbrains/jet/plugin/JetPluginUtil.java
+++ b/idea/src/org/jetbrains/jet/plugin/JetPluginUtil.java
@@ -23,8 +23,6 @@ import com.intellij.ide.plugins.IdeaPluginDescriptor;
 import com.intellij.ide.plugins.PluginManager;
 import com.intellij.openapi.extensions.PluginId;
 import com.intellij.openapi.module.Module;
-import com.intellij.openapi.module.ModuleManager;
-import com.intellij.openapi.module.ModuleUtil;
 import com.intellij.openapi.module.ModuleUtilCore;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.roots.ProjectFileIndex;
@@ -90,6 +88,10 @@ public class JetPluginUtil {
     }
 
     public static boolean isInSourceContent(@NotNull PsiElement element) {
+        return isInSourceContent(element, true);
+    }
+
+    public static boolean isInSourceContent(@NotNull PsiElement element, boolean includeLibrarySources) {
         PsiFile containingFile = element.getContainingFile();
         if (containingFile == null) {
             return false;
@@ -98,7 +100,8 @@ public class JetPluginUtil {
         if (virtualFile == null) {
             return false;
         }
-        return ProjectFileIndex.SERVICE.getInstance(element.getProject()).isInSourceContent(virtualFile);
+        ProjectFileIndex index = ProjectFileIndex.SERVICE.getInstance(element.getProject());
+        return includeLibrarySources ? index.isInSource(virtualFile) : index.isInSourceContent(virtualFile);
     }
 
     public static boolean isInSource(@NotNull PsiElement element) {
diff --git a/idea/src/org/jetbrains/jet/plugin/highlighter/JetPsiChecker.java b/idea/src/org/jetbrains/jet/plugin/highlighter/JetPsiChecker.java
index 7213b0400fd..1eb12eee227 100644
--- a/idea/src/org/jetbrains/jet/plugin/highlighter/JetPsiChecker.java
+++ b/idea/src/org/jetbrains/jet/plugin/highlighter/JetPsiChecker.java
@@ -115,7 +115,7 @@ public class JetPsiChecker implements Annotator {
             try {
                 BindingContext bindingContext = AnalyzerFacadeWithCache.analyzeFileWithCache(file).getBindingContext();
 
-                if (errorReportingEnabled) {
+                if (errorReportingEnabled && JetPluginUtil.isInSourceContent(element, false)) {
                     Collection<Diagnostic> diagnostics = Sets.newLinkedHashSet(bindingContext.getDiagnostics());
                     Set<PsiElement> redeclarations = Sets.newHashSet();
                     for (Diagnostic diagnostic : diagnostics) {