diff --git a/idea/src/org/jetbrains/kotlin/idea/inspections/UnusedSymbolInspection.kt b/idea/src/org/jetbrains/kotlin/idea/inspections/UnusedSymbolInspection.kt
index 5bdfaca7b0f..da9c353612c 100644
--- a/idea/src/org/jetbrains/kotlin/idea/inspections/UnusedSymbolInspection.kt
+++ b/idea/src/org/jetbrains/kotlin/idea/inspections/UnusedSymbolInspection.kt
@@ -61,6 +61,7 @@ import com.intellij.refactoring.safeDelete.SafeDeleteHandler
 import org.jetbrains.kotlin.psi.JetPsiUtil
 import org.jetbrains.kotlin.psi.JetObjectDeclaration
 import org.jetbrains.kotlin.psi.JetClassOrObject
+import org.jetbrains.kotlin.idea.util.ProjectRootsUtil
 
 public class UnusedSymbolInspection : AbstractKotlinInspection() {
     private val javaInspection = UnusedDeclarationInspection()
@@ -92,6 +93,8 @@ public class UnusedSymbolInspection : AbstractKotlinInspection() {
                     else -> return
                 }
 
+                if (!ProjectRootsUtil.isInProjectSource(declaration)) return
+
                 // Simple PSI-based checks
                 if (declaration.getName() == null) return
                 if (declaration is JetEnumEntry) return