diff --git a/src/frontends/qt/GuiWorkArea.cpp b/src/frontends/qt/GuiWorkArea.cpp
index c643a30192..0535ee70d1 100644
--- a/src/frontends/qt/GuiWorkArea.cpp
+++ b/src/frontends/qt/GuiWorkArea.cpp
@@ -1037,7 +1037,7 @@ bool CompressorProxy::emitCheck(bool isAutoRepeat)
 }
 
 
-void CompressorProxy::slot(KeySymbol sym, KeyModifier mod, bool isAutoRepeat)
+void CompressorProxy::slot(KeySymbol const & sym, KeyModifier mod, bool isAutoRepeat)
 {
 	if (emitCheck(isAutoRepeat))
 		Q_EMIT signal(sym, mod);
diff --git a/src/frontends/qt/GuiWorkArea.h b/src/frontends/qt/GuiWorkArea.h
index 4d9e64d53f..391c311243 100644
--- a/src/frontends/qt/GuiWorkArea.h
+++ b/src/frontends/qt/GuiWorkArea.h
@@ -102,7 +102,7 @@ Q_SIGNALS:
 	///
 	void bufferViewChanged();
 	/// send key event to CompressorProxy
-	void compressKeySym(KeySymbol sym, KeyModifier mod, bool isAutoRepeat);
+	void compressKeySym(KeySymbol const & sym, KeyModifier mod, bool isAutoRepeat);
 
 private Q_SLOTS:
 	/// Scroll the BufferView.
@@ -170,9 +170,9 @@ class CompressorProxy : public QObject
 	bool emitCheck(bool isAutoRepeat);
 	bool flag_;
 	// input: event to compress
-	Q_SLOT void slot(KeySymbol sym, KeyModifier mod, bool isAutoRepeat);
+	Q_SLOT void slot(KeySymbol const & sym, KeyModifier mod, bool isAutoRepeat);
 	// output: compressed event
-    Q_SIGNAL void signal(KeySymbol sym, KeyModifier mod);
+    Q_SIGNAL void signal(KeySymbol const & sym, KeyModifier mod);
 public:
     // No default constructor, since the proxy must be a child of the
     // target object.