diff --git a/stepmania/src/Makefile.am b/stepmania/src/Makefile.am
index b2e95f2cce..7eaea6c0d5 100644
--- a/stepmania/src/Makefile.am
+++ b/stepmania/src/Makefile.am
@@ -50,8 +50,8 @@ ScreenTitleMenu.cpp ScreenTitleMenu.h ScreenUnlock.cpp ScreenUnlock.h ScreenWith
 DataStructures = \
 Attack.cpp Attack.h BannerCache.cpp BannerCache.h CatalogXml.cpp CatalogXml.h \
 Character.cpp Character.h CharacterHead.cpp CharacterHead.h \
-CodeDetector.cpp CodeDetector.h EnumHelper.cpp EnumHelper.h Course.cpp Course.h CourseUtil.cpp CourseUtil.h \
-Font.cpp Font.h FontCharAliases.cpp FontCharAliases.h \
+CodeDetector.cpp CodeDetector.h Difficulty.cpp Difficulty.h EnumHelper.cpp EnumHelper.h Course.cpp Course.h \
+CourseUtil.cpp CourseUtil.h Font.cpp Font.h FontCharAliases.cpp FontCharAliases.h \
 FontCharmaps.cpp FontCharmaps.h Game.h GameConstantsAndTypes.cpp GameConstantsAndTypes.h GameDef.cpp GameDef.h \
 GameInput.cpp GameInput.h Grade.cpp Grade.h HighScore.cpp HighScore.h Inventory.cpp Inventory.h LuaFunctions.h \
 LuaHelpers.cpp LuaHelpers.h LyricsLoader.cpp LyricsLoader.h MenuInput.h ModeChoice.cpp ModeChoice.h \