diff --git a/src/collection/collectionqueryoptions.h b/src/collection/collectionqueryoptions.h
index eb135dd5..785315ff 100644
--- a/src/collection/collectionqueryoptions.h
+++ b/src/collection/collectionqueryoptions.h
@@ -30,7 +30,7 @@ class CollectionQueryOptions {
   explicit CollectionQueryOptions();
 
   struct Where {
-    explicit Where(const QString _column = QString(), const QVariant _value = QString(), const QString _op = QString()) : column(_column), value(_value), op(_op) {}
+    explicit Where(const QString &_column = QString(), const QVariant &_value = QString(), const QString &_op = QString()) : column(_column), value(_value), op(_op) {}
     QString column;
     QVariant value;
     QString op;
diff --git a/src/covermanager/albumcoverloader.cpp b/src/covermanager/albumcoverloader.cpp
index c8a8233a..ae8a0d86 100644
--- a/src/covermanager/albumcoverloader.cpp
+++ b/src/covermanager/albumcoverloader.cpp
@@ -251,7 +251,7 @@ void AlbumCoverLoader::InitArt(TaskPtr task) {
 
 }
 
-AlbumCoverLoader::LoadImageResult AlbumCoverLoader::LoadImage(TaskPtr task, const AlbumCoverLoaderOptions::Type &type) {
+AlbumCoverLoader::LoadImageResult AlbumCoverLoader::LoadImage(TaskPtr task, const AlbumCoverLoaderOptions::Type type) {
 
   switch (type) {
     case AlbumCoverLoaderOptions::Type::Unset:{
diff --git a/src/covermanager/albumcoverloader.h b/src/covermanager/albumcoverloader.h
index ffe7faf3..7f47b5d1 100644
--- a/src/covermanager/albumcoverloader.h
+++ b/src/covermanager/albumcoverloader.h
@@ -109,7 +109,7 @@ class AlbumCoverLoader : public QObject {
   quint64 EnqueueTask(TaskPtr task);
   void ProcessTask(TaskPtr task);
   void InitArt(TaskPtr task);
-  LoadImageResult LoadImage(TaskPtr task, const AlbumCoverLoaderOptions::Type &type);
+  LoadImageResult LoadImage(TaskPtr task, const AlbumCoverLoaderOptions::Type type);
   LoadImageResult LoadEmbeddedImage(TaskPtr task);
   LoadImageResult LoadUrlImage(TaskPtr task, const AlbumCoverLoaderResult::Type result_type, const QUrl &cover_url);
   LoadImageResult LoadLocalUrlImage(TaskPtr task, const AlbumCoverLoaderResult::Type result_type, const QUrl &cover_url);
diff --git a/src/covermanager/albumcoverloaderresult.h b/src/covermanager/albumcoverloaderresult.h
index 360968b2..f43e8b39 100644
--- a/src/covermanager/albumcoverloaderresult.h
+++ b/src/covermanager/albumcoverloaderresult.h
@@ -41,10 +41,10 @@ class AlbumCoverLoaderResult {
 
   explicit AlbumCoverLoaderResult(const bool _success = false,
                                   const Type _type = Type::None,
-                                  AlbumCoverImageResult _album_cover = AlbumCoverImageResult(),
+                                  const AlbumCoverImageResult &_album_cover = AlbumCoverImageResult(),
                                   const QImage &_image_scaled = QImage(),
-                                  const QUrl _art_manual_updated = QUrl(),
-                                  const QUrl _art_automatic_updated = QUrl()) :
+                                  const QUrl &_art_manual_updated = QUrl(),
+                                  const QUrl &_art_automatic_updated = QUrl()) :
                                   success(_success),
                                   type(_type),
                                   album_cover(_album_cover),
diff --git a/src/lyrics/azlyricscomlyricsprovider.cpp b/src/lyrics/azlyricscomlyricsprovider.cpp
index 1f02f47d..690532c9 100644
--- a/src/lyrics/azlyricscomlyricsprovider.cpp
+++ b/src/lyrics/azlyricscomlyricsprovider.cpp
@@ -44,7 +44,7 @@ QUrl AzLyricsComLyricsProvider::Url(const LyricsSearchRequest &request) {
 
 }
 
-QString AzLyricsComLyricsProvider::StringFixup(QString text) {
+QString AzLyricsComLyricsProvider::StringFixup(const QString &text) {
 
   return Utilities::Transliterate(text).remove(QRegularExpression("[^\\w0-9\\-]")).toLower();
 
diff --git a/src/lyrics/azlyricscomlyricsprovider.h b/src/lyrics/azlyricscomlyricsprovider.h
index 823ddffd..11e2a35b 100644
--- a/src/lyrics/azlyricscomlyricsprovider.h
+++ b/src/lyrics/azlyricscomlyricsprovider.h
@@ -42,7 +42,7 @@ class AzLyricsComLyricsProvider : public HtmlLyricsProvider {
   QUrl Url(const LyricsSearchRequest &request) override;
 
  private:
-  QString StringFixup(QString text);
+  QString StringFixup(const QString &text);
 
  private:
   static const char kUrl[];
diff --git a/src/lyrics/elyricsnetlyricsprovider.cpp b/src/lyrics/elyricsnetlyricsprovider.cpp
index ca061a4c..e7c981d5 100644
--- a/src/lyrics/elyricsnetlyricsprovider.cpp
+++ b/src/lyrics/elyricsnetlyricsprovider.cpp
@@ -44,7 +44,7 @@ QUrl ElyricsNetLyricsProvider::Url(const LyricsSearchRequest &request) {
 
 }
 
-QString ElyricsNetLyricsProvider::StringFixup(QString text) {
+QString ElyricsNetLyricsProvider::StringFixup(const QString &text) {
 
   return Utilities::Transliterate(text)
     .replace(QRegularExpression("[^\\w0-9_,&\\-\\(\\) ]"), "_")
diff --git a/src/lyrics/elyricsnetlyricsprovider.h b/src/lyrics/elyricsnetlyricsprovider.h
index 769fc8b2..bf030514 100644
--- a/src/lyrics/elyricsnetlyricsprovider.h
+++ b/src/lyrics/elyricsnetlyricsprovider.h
@@ -42,7 +42,7 @@ class ElyricsNetLyricsProvider : public HtmlLyricsProvider {
   QUrl Url(const LyricsSearchRequest &request) override;
 
  private:
-  QString StringFixup(QString text);
+  QString StringFixup(const QString &text);
 
  private:
   static const char kUrl[];
diff --git a/src/playlist/playlistfilterparser.cpp b/src/playlist/playlistfilterparser.cpp
index 834e7eab..b97f5e1d 100644
--- a/src/playlist/playlistfilterparser.cpp
+++ b/src/playlist/playlistfilterparser.cpp
@@ -131,7 +131,7 @@ class FloatEqComparator : public SearchTermComparator {
 
 class FloatNeComparator : public SearchTermComparator {
  public:
-  explicit FloatNeComparator(const float &value) : search_term_(value) {}
+  explicit FloatNeComparator(const float value) : search_term_(value) {}
   bool Matches(const QString &element) const override {
     return search_term_ != element.toFloat();
   }
@@ -141,7 +141,7 @@ class FloatNeComparator : public SearchTermComparator {
 
 class FloatGtComparator : public SearchTermComparator {
  public:
-  explicit FloatGtComparator(const float &value) : search_term_(value) {}
+  explicit FloatGtComparator(const float value) : search_term_(value) {}
   bool Matches(const QString &element) const override {
     return element.toFloat() > search_term_;
   }
@@ -151,7 +151,7 @@ class FloatGtComparator : public SearchTermComparator {
 
 class FloatGeComparator : public SearchTermComparator {
  public:
-  explicit FloatGeComparator(const float &value) : search_term_(value) {}
+  explicit FloatGeComparator(const float value) : search_term_(value) {}
   bool Matches(const QString &element) const override {
     return element.toFloat() >= search_term_;
   }
@@ -161,7 +161,7 @@ class FloatGeComparator : public SearchTermComparator {
 
 class FloatLtComparator : public SearchTermComparator {
  public:
-  explicit FloatLtComparator(const float &value) : search_term_(value) {}
+  explicit FloatLtComparator(const float value) : search_term_(value) {}
   bool Matches(const QString &element) const override {
     return element.toFloat() < search_term_;
   }
@@ -171,7 +171,7 @@ class FloatLtComparator : public SearchTermComparator {
 
 class FloatLeComparator : public SearchTermComparator {
  public:
-  explicit FloatLeComparator(const float &value) : search_term_(value) {}
+  explicit FloatLeComparator(const float value) : search_term_(value) {}
   bool Matches(const QString &element) const override {
     return element.toFloat() <= search_term_;
   }