diff --git a/mkspecs/features/common_pre.prf b/mkspecs/features/common_pre.prf
index e2dc89032..abfa3753b 100644
--- a/mkspecs/features/common_pre.prf
+++ b/mkspecs/features/common_pre.prf
@@ -74,7 +74,12 @@ msvc:!llvm: QMAKE_CXXFLAGS *= /bigobj
 # No gigantic MinGW obj files
 ################################
 
-win32-g++: QMAKE_CXXFLAGS_DEBUG += -Og
+# If you get variables, optimized out during debugging, try to comment the first and uncomment
+# the second line. This disables all debug optimizations. But be warned, that the build
+# will take hours.
+
+win32-g++: CONFIG += optimize_debug
+# win32-g++: QMAKE_CXXFLAGS *= -Wa,-mbig-obj
 
 ################################
 # FSX or FS9 on 32bit Windows only
diff --git a/src/blackmisc/metaclass.h b/src/blackmisc/metaclass.h
index 8a49a39f7..0d6a6bb60 100644
--- a/src/blackmisc/metaclass.h
+++ b/src/blackmisc/metaclass.h
@@ -28,7 +28,7 @@
 
 // Work around MinGW problem with combination of constexpr and extern template
 #if defined(Q_OS_WIN) && defined(Q_CC_GNU)
-#define BLACK_NO_EXPORT_CONSTEXPR constexpr inline __attribute__((gnu_inline))
+#define BLACK_NO_EXPORT_CONSTEXPR constexpr inline __attribute__((always_inline))
 #else
 #define BLACK_NO_EXPORT_CONSTEXPR constexpr
 #endif