diff --git a/src/sfizz/Synth.cpp b/src/sfizz/Synth.cpp
index 1bd10f69..879816b1 100644
--- a/src/sfizz/Synth.cpp
+++ b/src/sfizz/Synth.cpp
@@ -1905,7 +1905,7 @@ BitArray<config::numCCs> Synth::Impl::collectAllUsedCCs()
     return used;
 }
 
-const std::string* Synth::Impl::getKeyLabel(int keyNumber)
+const std::string* Synth::Impl::getKeyLabel(int keyNumber) const
 {
     auto it = keyLabelsMap_.find(keyNumber);
     return (it == keyLabelsMap_.end()) ? nullptr : &keyLabels_[it->second].second;
@@ -1923,7 +1923,7 @@ void Synth::Impl::setKeyLabel(int keyNumber, std::string name)
     }
 }
 
-const std::string* Synth::Impl::getCCLabel(int ccNumber)
+const std::string* Synth::Impl::getCCLabel(int ccNumber) const
 {
     auto it = ccLabelsMap_.find(ccNumber);
     return (it == ccLabelsMap_.end()) ? nullptr : &ccLabels_[it->second].second;
@@ -1941,7 +1941,7 @@ void Synth::Impl::setCCLabel(int ccNumber, std::string name)
     }
 }
 
-const std::string* Synth::Impl::getKeyswitchLabel(int swNumber)
+const std::string* Synth::Impl::getKeyswitchLabel(int swNumber) const
 {
     auto it = keyswitchLabelsMap_.find(swNumber);
     return (it == keyswitchLabelsMap_.end()) ? nullptr : &keyswitchLabels_[it->second].second;
diff --git a/src/sfizz/SynthPrivate.h b/src/sfizz/SynthPrivate.h
index bfc3344a..502f548b 100644
--- a/src/sfizz/SynthPrivate.h
+++ b/src/sfizz/SynthPrivate.h
@@ -181,13 +181,13 @@ struct Synth::Impl final: public Parser::Listener {
 
     BitArray<config::numCCs> collectAllUsedCCs();
 
-    const std::string* getKeyLabel(int keyNumber);
+    const std::string* getKeyLabel(int keyNumber) const;
     void setKeyLabel(int keyNumber, std::string name);
     void clearKeyLabels();
-    const std::string* getCCLabel(int ccNumber);
+    const std::string* getCCLabel(int ccNumber) const;
     void setCCLabel(int ccNumber, std::string name);
     void clearCCLabels();
-    const std::string* getKeyswitchLabel(int swNumber);
+    const std::string* getKeyswitchLabel(int swNumber) const;
     void setKeyswitchLabel(int swNumber, std::string name);
     void clearKeyswitchLabels();