diff --git a/CMakeLists.txt b/CMakeLists.txt
index e38c1db9b..e28d28f38 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -198,7 +198,7 @@ if( CMAKE_CXX_COMPILER_ID MATCHES "Clang" )
     )
         string( APPEND CMAKE_CXX_FLAGS " ${CLANG_WARNINGS}" )
     endforeach()
-    set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DNOTREACHED='//'" )
+    set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DNOTREACHED='//' -DFALLTHRU='[[clang::fallthrough]]'")
 
     # Third-party code where we don't care so much about compiler warnings
     # (because it's uncomfortable to patch) get different flags; use
@@ -225,7 +225,7 @@ else()
     set( SUPPRESS_3RDPARTY_WARNINGS "" )
     set( SUPPRESS_BOOST_WARNINGS "" )
 
-    set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DNOTREACHED='__builtin_unreachable();'" )
+    set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DNOTREACHED='__builtin_unreachable();' -DFALLTHRU='/* */'" )
 endif()
 
 # Use mark_thirdparty_code() to reduce warnings from the compiler
diff --git a/src/modules/packagechooser/PackageChooserPage.cpp b/src/modules/packagechooser/PackageChooserPage.cpp
index 0587af190..6f565c914 100644
--- a/src/modules/packagechooser/PackageChooserPage.cpp
+++ b/src/modules/packagechooser/PackageChooserPage.cpp
@@ -41,9 +41,12 @@ PackageChooserPage::PackageChooserPage( PackageChooserMode mode, QWidget* parent
     switch ( mode )
     {
     case PackageChooserMode::Optional:
+        FALLTHRU;
     case PackageChooserMode::Required:
         ui->products->setSelectionMode( QAbstractItemView::SingleSelection );
+        break;
     case PackageChooserMode::OptionalMultiple:
+        FALLTHRU;
     case PackageChooserMode::RequiredMultiple:
         ui->products->setSelectionMode( QAbstractItemView::ExtendedSelection );
     }