diff --git a/sfizz/Synth.cpp b/sfizz/Synth.cpp
index 721f6b70..fc79c512 100644
--- a/sfizz/Synth.cpp
+++ b/sfizz/Synth.cpp
@@ -293,13 +293,14 @@ sfz::Voice* sfz::Synth::findFreeVoice() noexcept
     return {};
 }
 
-void sfz::Synth::getNumActiveVoices() const noexcept
+int sfz::Synth::getNumActiveVoices() const noexcept
 {
     auto activeVoices { 0 };
     for (const auto& voice : voices) {
         if (!voice->isFree())
             activeVoices++;
     }
+    return activeVoices;
 }
 
 void sfz::Synth::garbageCollect() noexcept
diff --git a/sfizz/Synth.h b/sfizz/Synth.h
index 24fd9604..13c10e9e 100644
--- a/sfizz/Synth.h
+++ b/sfizz/Synth.h
@@ -59,7 +59,7 @@ public:
     void aftertouch(int delay, int channel, uint8_t aftertouch) noexcept;
     void tempo(int delay, float secondsPerQuarter) noexcept;
 
-    void getNumActiveVoices() const noexcept;
+    int getNumActiveVoices() const noexcept;
     void garbageCollect() noexcept;
 protected:
     void callback(absl::string_view header, const std::vector<Opcode>& members) final;