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

Index: al/effects/modulator.cpp
--- al/effects/modulator.cpp.orig
+++ al/effects/modulator.cpp
@@ -39,9 +39,10 @@ constexpr ALenum EnumFromWaveform(ModulatorWaveform ty
     case ModulatorWaveform::Sinusoid: return AL_RING_MODULATOR_SINUSOID;
     case ModulatorWaveform::Sawtooth: return AL_RING_MODULATOR_SAWTOOTH;
     case ModulatorWaveform::Square: return AL_RING_MODULATOR_SQUARE;
+    default:
+        throw std::runtime_error{fmt::format("Invalid modulator waveform: {}",
+            int{al::to_underlying(type)})};
     }
-    throw std::runtime_error{fmt::format("Invalid modulator waveform: {}",
-        int{al::to_underlying(type)})};
 }
 
 constexpr EffectProps genDefaultProps() noexcept
