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

Index: al/effects/vmorpher.cpp
--- al/effects/vmorpher.cpp.orig
+++ al/effects/vmorpher.cpp
@@ -96,8 +96,9 @@ constexpr ALenum EnumFromPhenome(VMorpherPhenome pheno
     HANDLE_PHENOME(T);
     HANDLE_PHENOME(V);
     HANDLE_PHENOME(Z);
+    default:
+        throw std::runtime_error{fmt::format("Invalid phenome: {}", int{al::to_underlying(phenome)})};
     }
-    throw std::runtime_error{fmt::format("Invalid phenome: {}", int{al::to_underlying(phenome)})};
 #undef HANDLE_PHENOME
 }
 
@@ -118,9 +119,10 @@ constexpr ALenum EnumFromWaveform(VMorpherWaveform typ
     case VMorpherWaveform::Sinusoid: return AL_VOCAL_MORPHER_WAVEFORM_SINUSOID;
     case VMorpherWaveform::Triangle: return AL_VOCAL_MORPHER_WAVEFORM_TRIANGLE;
     case VMorpherWaveform::Sawtooth: return AL_VOCAL_MORPHER_WAVEFORM_SAWTOOTH;
+    default:
+        throw std::runtime_error{fmt::format("Invalid vocal morpher waveform: {}",
+            int{al::to_underlying(type)})};
     }
-    throw std::runtime_error{fmt::format("Invalid vocal morpher waveform: {}",
-        int{al::to_underlying(type)})};
 }
 
 constexpr EffectProps genDefaultProps() noexcept
