diff --git a/Userland/Libraries/LibDSP/Envelope.h b/Userland/Libraries/LibDSP/Envelope.h
index 85a2716b59..a21ccbeefe 100644
--- a/Userland/Libraries/LibDSP/Envelope.h
+++ b/Userland/Libraries/LibDSP/Envelope.h
@@ -50,7 +50,7 @@ struct Envelope {
 
     constexpr void reset() { envelope = -1; }
 
-    constexpr operator EnvelopeState()
+    constexpr operator EnvelopeState() const
     {
         if (!is_active())
             return EnvelopeState::Off;
diff --git a/Userland/Libraries/LibDSP/Synthesizers.cpp b/Userland/Libraries/LibDSP/Synthesizers.cpp
index 4a3988d067..69f2ad65a5 100644
--- a/Userland/Libraries/LibDSP/Synthesizers.cpp
+++ b/Userland/Libraries/LibDSP/Synthesizers.cpp
@@ -64,7 +64,7 @@ Signal Classic::process_impl(Signal const& input_signal)
 }
 
 // Linear ADSR envelope with no peak adjustment.
-double Classic::volume_from_envelope(Envelope envelope)
+double Classic::volume_from_envelope(Envelope const& envelope)
 {
     switch (static_cast<EnvelopeState>(envelope)) {
     case EnvelopeState::Off:
diff --git a/Userland/Libraries/LibDSP/Synthesizers.h b/Userland/Libraries/LibDSP/Synthesizers.h
index 3d89e014a6..1a7ebed6a6 100644
--- a/Userland/Libraries/LibDSP/Synthesizers.h
+++ b/Userland/Libraries/LibDSP/Synthesizers.h
@@ -49,7 +49,7 @@ public:
 private:
     virtual Signal process_impl(Signal const&) override;
 
-    double volume_from_envelope(Envelope);
+    double volume_from_envelope(Envelope const&);
     double wave_position(u8 note);
     double samples_per_cycle(u8 note);
     double sin_position(u8 note);