diff --git a/src/actions.cpp b/src/actions.cpp
index 49087996..847b73e8 100644
--- a/src/actions.cpp
+++ b/src/actions.cpp
@@ -1564,14 +1564,18 @@ void ToggleScreenLock::run()
 {
 	using Global::wFooter;
 	using Global::myLockedScreen;
-	// FIXME: check if screen can be locked before prompting for width
-	if (myLockedScreen != 0)
+	const char *msg_unlockable_screen = "Current screen can't be locked";
+	if (myLockedScreen != nullptr)
 	{
 		BaseScreen::unlock();
 		Actions::setResizeFlags();
 		myScreen->resize();
 		Statusbar::print("Screen unlocked");
 	}
+	else if (!myScreen->isLockable())
+	{
+		Statusbar::print(msg_unlockable_screen);
+	}
 	else
 	{
 		unsigned part = Config.locked_screen_width_part*100;
@@ -1586,7 +1590,7 @@ void ToggleScreenLock::run()
 		if (myScreen->lock())
 			Statusbar::printf("Screen locked (with %1%%% width)", part);
 		else
-			Statusbar::print("Current screen can't be locked");
+			Statusbar::print(msg_unlockable_screen);
 	}
 }
 
diff --git a/src/browser.h b/src/browser.h
index b310ce51..9cbf9f04 100644
--- a/src/browser.h
+++ b/src/browser.h
@@ -43,6 +43,7 @@ struct Browser: Screen<NC::Menu<MPD::Item>>, HasSongs, Searchable, Tabbable
 	virtual void spacePressed() OVERRIDE;
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// Searchable implementation
@@ -73,9 +74,6 @@ struct Browser: Screen<NC::Menu<MPD::Item>>, HasSongs, Searchable, Tabbable
 
 	static void fetchSupportedExtensions();
 
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
-	
 private:
 	bool m_update_request;
 	bool m_local_browser;
diff --git a/src/clock.h b/src/clock.h
index 119abef5..5f44aa15 100644
--- a/src/clock.h
+++ b/src/clock.h
@@ -46,10 +46,8 @@ struct Clock: Screen<NC::Window>, Tabbable
 	virtual void spacePressed() OVERRIDE { }
 	virtual void mouseButtonPressed(MEVENT) OVERRIDE { }
 	
-	virtual bool isMergable() OVERRIDE { return true; }
-	
-protected:
 	virtual bool isLockable() OVERRIDE { return false; }
+	virtual bool isMergable() OVERRIDE { return true; }
 	
 private:
 	NC::Window m_pane;
diff --git a/src/help.h b/src/help.h
index eef1d047..0a3ed220 100644
--- a/src/help.h
+++ b/src/help.h
@@ -40,10 +40,8 @@ struct Help: Screen<NC::Scrollpad>, Tabbable
 	virtual void enterPressed() OVERRIDE { }
 	virtual void spacePressed() OVERRIDE { }
 	
-	virtual bool isMergable() OVERRIDE { return true; }
-	
-protected:
 	virtual bool isLockable() OVERRIDE { return true; }
+	virtual bool isMergable() OVERRIDE { return true; }
 };
 
 extern Help *myHelp;
diff --git a/src/lastfm.h b/src/lastfm.h
index 051dc8aa..09638824 100644
--- a/src/lastfm.h
+++ b/src/lastfm.h
@@ -48,6 +48,7 @@ struct Lastfm: Screen<NC::Scrollpad>, Tabbable
 	virtual void enterPressed() OVERRIDE { }
 	virtual void spacePressed() OVERRIDE { }
 	
+	virtual bool isLockable() OVERRIDE { return false; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	template <typename ServiceT>
@@ -69,9 +70,6 @@ struct Lastfm: Screen<NC::Scrollpad>, Tabbable
 		m_title = ToWString(m_service->name());
 	}
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return false; }
-	
 private:
 	void getResult();
 	
diff --git a/src/lyrics.h b/src/lyrics.h
index bc5d5c5a..b5500566 100644
--- a/src/lyrics.h
+++ b/src/lyrics.h
@@ -45,6 +45,7 @@ struct Lyrics: Screen<NC::Scrollpad>, Tabbable
 	virtual void enterPressed() OVERRIDE { }
 	virtual void spacePressed() OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return false; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// private members
@@ -60,9 +61,6 @@ struct Lyrics: Screen<NC::Scrollpad>, Tabbable
 	
 	bool Reload;
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return false; }
-	
 private:
 	void Load();
 	
diff --git a/src/media_library.h b/src/media_library.h
index 97264743..9163c16c 100644
--- a/src/media_library.h
+++ b/src/media_library.h
@@ -46,6 +46,7 @@ struct MediaLibrary: Screen<NC::Window *>, HasColumns, HasSongs, Searchable, Tab
 	virtual void spacePressed() OVERRIDE;
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// Searchable implementation
@@ -135,9 +136,6 @@ struct MediaLibrary: Screen<NC::Window *>, HasColumns, HasSongs, Searchable, Tab
 	NC::Menu<AlbumEntry> Albums;
 	NC::Menu<MPD::Song> Songs;
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
-	
 private:
 	void AddToPlaylist(bool);
 
diff --git a/src/outputs.h b/src/outputs.h
index 9c55d196..c7817bbf 100644
--- a/src/outputs.h
+++ b/src/outputs.h
@@ -47,13 +47,11 @@ struct Outputs: Screen<NC::Menu<MPD::Output>>, Tabbable
 	virtual void spacePressed() OVERRIDE { }
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// private members
 	void FetchList();
-	
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
 };
 
 extern Outputs *myOutputs;
diff --git a/src/playlist.h b/src/playlist.h
index 081f24ad..ec7bf98a 100644
--- a/src/playlist.h
+++ b/src/playlist.h
@@ -46,6 +46,7 @@ struct Playlist: Screen<NC::Menu<MPD::Song>>, HasSongs, Searchable, Tabbable
 	virtual void spacePressed() OVERRIDE;
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// Searchable implementation
@@ -77,9 +78,6 @@ struct Playlist: Screen<NC::Menu<MPD::Song>>, HasSongs, Searchable, Tabbable
 	void reloadTotalLength() { m_reload_total_length = true; }
 	void reloadRemaining() { m_reload_remaining = true; }
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
-	
 private:
 	std::string getTotalLength();
 
diff --git a/src/playlist_editor.h b/src/playlist_editor.h
index d874fbbb..817cd33b 100644
--- a/src/playlist_editor.h
+++ b/src/playlist_editor.h
@@ -46,6 +46,7 @@ struct PlaylistEditor: Screen<NC::Window *>, HasColumns, HasSongs, Searchable, T
 	virtual void spacePressed() OVERRIDE;
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// Searchable implementation
@@ -80,9 +81,6 @@ struct PlaylistEditor: Screen<NC::Window *>, HasColumns, HasSongs, Searchable, T
 	NC::Menu<MPD::Playlist> Playlists;
 	NC::Menu<MPD::Song> Content;
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
-	
 private:
 	void AddToPlaylist(bool);
 	
diff --git a/src/screen.cpp b/src/screen.cpp
index 73122b7f..5c436941 100644
--- a/src/screen.cpp
+++ b/src/screen.cpp
@@ -98,8 +98,7 @@ void BaseScreen::getWindowResizeParams(size_t &x_offset, size_t &width, bool adj
 
 bool BaseScreen::lock()
 {
-	if (myLockedScreen)
-		return false;
+	assert(myLockedScreen == nullptr);
 	if (isLockable())
 	{
 		myLockedScreen = this;
diff --git a/src/screen.h b/src/screen.h
index a958d539..8ba52c7a 100644
--- a/src/screen.h
+++ b/src/screen.h
@@ -80,6 +80,12 @@ struct BaseScreen
 	
 	/// @see Screen::mouseButtonPressed()
 	virtual void mouseButtonPressed(MEVENT me) = 0;
+
+	/// @return true if screen can be locked. Note that returning
+	/// false here doesn't neccesarily mean that screen is also not
+	/// mergable (eg. lyrics screen is not lockable since that wouldn't
+	/// make much sense, but it's perfectly fine to merge it).
+	virtual bool isLockable() = 0;
 	
 	/// @return true if screen is mergable, ie. can be "proper" subwindow
 	/// if one of the screens is locked. Screens that somehow resemble popups
@@ -98,12 +104,6 @@ struct BaseScreen
 	static void unlock();
 	
 protected:
-	/// @return true if screen can be locked. Note that returning
-	/// false here doesn't neccesarily mean that screen is also not
-	/// mergable (eg. lyrics screen is not lockable since that wouldn't
-	/// make much sense, but it's perfectly fine to merge it).
-	virtual bool isLockable() = 0;
-	
 	/// Gets X offset and width of current screen to be used eg. in resize() function.
 	/// @param adjust_locked_screen indicates whether this function should
 	/// automatically adjust locked screen's dimensions (if there is one set)
diff --git a/src/search_engine.h b/src/search_engine.h
index e448ff11..0232540a 100644
--- a/src/search_engine.h
+++ b/src/search_engine.h
@@ -91,6 +91,7 @@ struct SearchEngine: Screen<NC::Menu<SEItem>>, HasSongs, Searchable, Tabbable
 	virtual void spacePressed() OVERRIDE;
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// Searchable implementation
@@ -113,9 +114,6 @@ struct SearchEngine: Screen<NC::Menu<SEItem>>, HasSongs, Searchable, Tabbable
 	static size_t SearchButton;
 	static size_t ResetButton;
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
-	
 private:
 	void Prepare();
 	void Search();
diff --git a/src/sel_items_adder.h b/src/sel_items_adder.h
index 525705a9..5adfcd5a 100644
--- a/src/sel_items_adder.h
+++ b/src/sel_items_adder.h
@@ -47,10 +47,8 @@ struct SelectedItemsAdder: Screen<NC::Menu<RunnableItem<std::string, void()>> *>
 	virtual void spacePressed() OVERRIDE { }
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
-	virtual bool isMergable() OVERRIDE { return false; }
-	
-protected:
 	virtual bool isLockable() OVERRIDE { return false; }
+	virtual bool isMergable() OVERRIDE { return false; }
 	
 private:
 	void populatePlaylistSelector(BaseScreen *screen);
diff --git a/src/server_info.h b/src/server_info.h
index 5213fcc0..54d0b362 100644
--- a/src/server_info.h
+++ b/src/server_info.h
@@ -42,10 +42,8 @@ struct ServerInfo: Screen<NC::Scrollpad>, Tabbable
 	virtual void enterPressed() OVERRIDE { }
 	virtual void spacePressed() OVERRIDE { }
 	
-	virtual bool isMergable() OVERRIDE { return false; }
-	
-protected:
 	virtual bool isLockable() OVERRIDE { return false; }
+	virtual bool isMergable() OVERRIDE { return false; }
 	
 private:
 	void SetDimensions();
diff --git a/src/song_info.h b/src/song_info.h
index 9c07261d..2933740a 100644
--- a/src/song_info.h
+++ b/src/song_info.h
@@ -48,14 +48,12 @@ struct SongInfo: Screen<NC::Scrollpad>, Tabbable
 	virtual void enterPressed() OVERRIDE { }
 	virtual void spacePressed() OVERRIDE { }
 	
+	virtual bool isLockable() OVERRIDE { return false; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// private members
 	static const Metadata Tags[];
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return false; }
-	
 private:
 	void PrepareSong(MPD::Song &);
 };
diff --git a/src/sort_playlist.h b/src/sort_playlist.h
index 32277496..9459c8ad 100644
--- a/src/sort_playlist.h
+++ b/src/sort_playlist.h
@@ -45,15 +45,13 @@ struct SortPlaylistDialog
 	virtual void spacePressed() OVERRIDE { }
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return false; }
 	virtual bool isMergable() OVERRIDE { return false; }
 	
 	// private members
 	void moveSortOrderUp();
 	void moveSortOrderDown();
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return false; }
-	
 private:
 	void moveSortOrderHint() const;
 	void sort() const;
diff --git a/src/tag_editor.h b/src/tag_editor.h
index 5e83990b..0ca0d8ee 100644
--- a/src/tag_editor.h
+++ b/src/tag_editor.h
@@ -49,6 +49,7 @@ struct TagEditor: Screen<NC::Window *>, HasColumns, HasSongs, Searchable, Tabbab
 	virtual void spacePressed() OVERRIDE;
 	virtual void mouseButtonPressed(MEVENT) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// Searchable implementation
@@ -79,9 +80,6 @@ struct TagEditor: Screen<NC::Window *>, HasColumns, HasSongs, Searchable, Tabbab
 	NC::Menu<std::string> *TagTypes;
 	NC::Menu<MPD::MutableSong> *Tags;
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
-	
 private:
 	void SetDimensions(size_t, size_t);
 	
diff --git a/src/tiny_tag_editor.h b/src/tiny_tag_editor.h
index 11e10c9b..53a32707 100644
--- a/src/tiny_tag_editor.h
+++ b/src/tiny_tag_editor.h
@@ -46,14 +46,12 @@ struct TinyTagEditor: Screen<NC::Menu<NC::Buffer>>
 	virtual void spacePressed() OVERRIDE { }
 	virtual void mouseButtonPressed(MEVENT me) OVERRIDE;
 	
+	virtual bool isLockable() OVERRIDE { return false; }
 	virtual bool isMergable() OVERRIDE { return true; }
 	
 	// private members
 	void SetEdited(const MPD::Song &);
 	
-protected:
-	virtual bool isLockable() OVERRIDE { return false; }
-	
 private:
 	bool getTags();
 	MPD::MutableSong itsEdited;
diff --git a/src/visualizer.h b/src/visualizer.h
index f6e028df..f756e955 100644
--- a/src/visualizer.h
+++ b/src/visualizer.h
@@ -53,6 +53,7 @@ struct Visualizer: Screen<NC::Window>, Tabbable
 	virtual void spacePressed() OVERRIDE;
 	virtual void mouseButtonPressed(MEVENT) OVERRIDE { }
 
+	virtual bool isLockable() OVERRIDE { return true; }
 	virtual bool isMergable() OVERRIDE { return true; }
 
 	// private members
@@ -60,9 +61,6 @@ struct Visualizer: Screen<NC::Window>, Tabbable
 	void ResetFD();
 	void FindOutputID();
 
-protected:
-	virtual bool isLockable() OVERRIDE { return true; }
-
 private:
 	void DrawSoundWave(int16_t *, ssize_t, size_t, size_t);
 	void DrawSoundWaveStereo(int16_t *, int16_t *, ssize_t, size_t);