gcc8: error: expression '<throw-expression>' is not a constant expression

Index: al/effects/fshifter.cpp
--- al/effects/fshifter.cpp.orig
+++ al/effects/fshifter.cpp
@@ -39,8 +39,9 @@ constexpr ALenum EnumFromDirection(FShifterDirection d
     case FShifterDirection::Down: return AL_FREQUENCY_SHIFTER_DIRECTION_DOWN;
     case FShifterDirection::Up: return AL_FREQUENCY_SHIFTER_DIRECTION_UP;
     case FShifterDirection::Off: return AL_FREQUENCY_SHIFTER_DIRECTION_OFF;
+    default:
+        throw std::runtime_error{fmt::format("Invalid direction: {}", int{al::to_underlying(dir)})};
     }
-    throw std::runtime_error{fmt::format("Invalid direction: {}", int{al::to_underlying(dir)})};
 }
 
 constexpr EffectProps genDefaultProps() noexcept
