diff --git a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
index e8ba441c271..6938a40bd34 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java
@@ -693,7 +693,7 @@ public interface Errors {
 
     DiagnosticFactory2<KtElement, KotlinType, KotlinType> INCOMPATIBLE_TYPES = DiagnosticFactory2.create(ERROR);
 
-    DiagnosticFactory0<PsiElement> IMPLICIT_NOTHING_RETURN_TYPE = DiagnosticFactory0.create(WARNING);
+    DiagnosticFactory0<PsiElement> IMPLICIT_NOTHING_RETURN_TYPE = DiagnosticFactory0.create(ERROR);
 
     // Context tracking