diff --git a/src/engine/enginebase.h b/src/engine/enginebase.h
index 00be606e..e7eb5768 100644
--- a/src/engine/enginebase.h
+++ b/src/engine/enginebase.h
@@ -126,10 +126,10 @@ class EngineBase : public QObject {
 
   virtual OutputDetailsList GetOutputsList() const = 0;
   virtual bool ValidOutput(const QString &output) = 0;
-  virtual QString DefaultOutput() = 0;
-  virtual bool CustomDeviceSupport(const QString &output) = 0;
-  virtual bool ALSADeviceSupport(const QString &output) = 0;
-  virtual bool ExclusiveModeSupport(const QString &output) = 0;
+  virtual QString DefaultOutput() const = 0;
+  virtual bool CustomDeviceSupport(const QString &output) const = 0;
+  virtual bool ALSADeviceSupport(const QString &output) const = 0;
+  virtual bool ExclusiveModeSupport(const QString &output) const = 0;
 
   // Plays a media stream represented with the URL 'u' from the given 'beginning' to the given 'end' (usually from 0 to a song's length).
   // Both markers should be passed in nanoseconds. 'end' can be negative, indicating that the real length of 'u' stream is unknown.
diff --git a/src/engine/gstengine.cpp b/src/engine/gstengine.cpp
index dea4076d..7ce63d79 100644
--- a/src/engine/gstengine.cpp
+++ b/src/engine/gstengine.cpp
@@ -454,15 +454,15 @@ bool GstEngine::ValidOutput(const QString &output) {
 
 }
 
-bool GstEngine::CustomDeviceSupport(const QString &output) {
+bool GstEngine::CustomDeviceSupport(const QString &output) const {
   return output == QLatin1String(kALSASink) || output == QLatin1String(kOpenALSASink) || output == QLatin1String(kOSSSink) || output == QLatin1String(kOSS4Sink) || output == QLatin1String(kPulseSink) || output == QLatin1String(kA2DPSink) || output == QLatin1String(kAVDTPSink) || output == QLatin1String(kJackAudioSink);
 }
 
-bool GstEngine::ALSADeviceSupport(const QString &output) {
+bool GstEngine::ALSADeviceSupport(const QString &output) const {
   return output == QLatin1String(kALSASink);
 }
 
-bool GstEngine::ExclusiveModeSupport(const QString &output) {
+bool GstEngine::ExclusiveModeSupport(const QString &output) const {
   return output == QLatin1String(kWASAPISink);
 }
 
diff --git a/src/engine/gstengine.h b/src/engine/gstengine.h
index cd865978..c23930ce 100644
--- a/src/engine/gstengine.h
+++ b/src/engine/gstengine.h
@@ -78,10 +78,10 @@ class GstEngine : public EngineBase, public GstBufferConsumer {
 
   OutputDetailsList GetOutputsList() const override;
   bool ValidOutput(const QString &output) override;
-  QString DefaultOutput() override { return QLatin1String(kAutoSink); }
-  bool CustomDeviceSupport(const QString &output) override;
-  bool ALSADeviceSupport(const QString &output) override;
-  bool ExclusiveModeSupport(const QString &output) override;
+  QString DefaultOutput() const override { return QLatin1String(kAutoSink); }
+  bool CustomDeviceSupport(const QString &output) const override;
+  bool ALSADeviceSupport(const QString &output) const override;
+  bool ExclusiveModeSupport(const QString &output) const override;
 
   void SetStartup(GstStartup *gst_startup) { gst_startup_ = gst_startup; }
   void EnsureInitialized() { gst_startup_->EnsureInitialized(); }
diff --git a/src/engine/vlcengine.cpp b/src/engine/vlcengine.cpp
index 332d1b48..b652e70a 100644
--- a/src/engine/vlcengine.cpp
+++ b/src/engine/vlcengine.cpp
@@ -255,15 +255,15 @@ bool VLCEngine::ValidOutput(const QString &output) {
 
 }
 
-bool VLCEngine::CustomDeviceSupport(const QString &output) {
-  return (output != QLatin1String("auto"));
+bool VLCEngine::CustomDeviceSupport(const QString &output) const {
+  return output != QLatin1String("auto");
 }
 
-bool VLCEngine::ALSADeviceSupport(const QString &output) {
-  return (output == QLatin1String("alsa"));
+bool VLCEngine::ALSADeviceSupport(const QString &output) const {
+  return output == QLatin1String("alsa");
 }
 
-bool VLCEngine::ExclusiveModeSupport(const QString &output) {
+bool VLCEngine::ExclusiveModeSupport(const QString &output) const {
   Q_UNUSED(output);
   return false;
 }
diff --git a/src/engine/vlcengine.h b/src/engine/vlcengine.h
index 50e991a0..04e3712f 100644
--- a/src/engine/vlcengine.h
+++ b/src/engine/vlcengine.h
@@ -67,10 +67,10 @@ class VLCEngine : public EngineBase {
 
   OutputDetailsList GetOutputsList() const override;
   bool ValidOutput(const QString &output) override;
-  QString DefaultOutput() override { return QLatin1String(""); }
-  bool CustomDeviceSupport(const QString &output) override;
-  bool ALSADeviceSupport(const QString &output) override;
-  bool ExclusiveModeSupport(const QString &output) override;
+  QString DefaultOutput() const override { return QLatin1String(""); }
+  bool CustomDeviceSupport(const QString &output) const override;
+  bool ALSADeviceSupport(const QString &output) const override;
+  bool ExclusiveModeSupport(const QString &output) const override;
 
  private:
   libvlc_instance_t *instance_;