diff --git a/platform/core-impl/src/com/intellij/psi/impl/file/impl/FileManager.java b/platform/core-impl/src/com/intellij/psi/impl/file/impl/FileManager.java
index 857c4140a10a..c15c1da03f03 100644
--- a/platform/core-impl/src/com/intellij/psi/impl/file/impl/FileManager.java
+++ b/platform/core-impl/src/com/intellij/psi/impl/file/impl/FileManager.java
@@ -47,7 +47,7 @@ public interface FileManager {
   void cleanupForNextTest();
 
   // todo IJPL-339 mark deprecated?
-  FileViewProvider findViewProvider(@NotNull VirtualFile vFile);
+  @NotNull FileViewProvider findViewProvider(@NotNull VirtualFile vFile);
 
   @ApiStatus.Experimental
   FileViewProvider findViewProvider(@NotNull VirtualFile vFile, @NotNull CodeInsightContext context);
diff --git a/platform/lang-impl/src/com/intellij/mock/MockFileManager.java b/platform/lang-impl/src/com/intellij/mock/MockFileManager.java
index 545b477c1725..bc7bcbd6c888 100644
--- a/platform/lang-impl/src/com/intellij/mock/MockFileManager.java
+++ b/platform/lang-impl/src/com/intellij/mock/MockFileManager.java
@@ -84,7 +84,7 @@ public final class MockFileManager implements FileManager {
   }
 
   @Override
-  public FileViewProvider findViewProvider(@NotNull VirtualFile vFile) {
+  public @NotNull FileViewProvider findViewProvider(@NotNull VirtualFile vFile) {
     throw new UnsupportedOperationException("Method findViewProvider is not yet implemented in " + getClass().getName());
   }