diff --git a/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/JetClassAnnotation.java b/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/JetClassAnnotation.java
index 5f0c988d954..811bf01b4c4 100644
--- a/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/JetClassAnnotation.java
+++ b/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/JetClassAnnotation.java
@@ -41,6 +41,7 @@ public class JetClassAnnotation extends PsiAnnotationWithFlags {
         signature = getStringAttribute(JvmStdlibNames.JET_CLASS_SIGNATURE, "");
     }
 
+    @NotNull
     public String signature() {
         checkInitialized();
         return signature;
diff --git a/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/KotlinSignatureAnnotation.java b/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/KotlinSignatureAnnotation.java
index 09bbbdff2ae..4828e53745c 100644
--- a/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/KotlinSignatureAnnotation.java
+++ b/compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/kt/KotlinSignatureAnnotation.java
@@ -41,6 +41,7 @@ public class KotlinSignatureAnnotation extends PsiAnnotationWrapper {
         signature = StringUtil.unescapeStringCharacters(getStringAttribute(JvmStdlibNames.KOTLIN_SIGNATURE_VALUE_METHOD, ""));
     }
 
+    @NotNull
     public String signature() {
         checkInitialized();
         return signature;