diff --git a/sources/Parser.h b/sources/Parser.h
index a72cc930..9462d2f1 100644
--- a/sources/Parser.h
+++ b/sources/Parser.h
@@ -27,7 +27,7 @@ public:
     void disableRecursiveIncludeGuard() { recursiveIncludeGuard = false; }
     void enableRecursiveIncludeGuard() { recursiveIncludeGuard = true; }
 protected:
-    virtual void callback(std::string_view header, std::vector<Opcode> members) = 0;
+    virtual void callback(std::string_view header, const std::vector<Opcode>& members) = 0;
     std::filesystem::path rootDirectory { std::filesystem::current_path() };
 private:
     bool recursiveIncludeGuard { false };
diff --git a/sources/ParserMain.cpp b/sources/ParserMain.cpp
index 990487c5..fc75cb5d 100644
--- a/sources/ParserMain.cpp
+++ b/sources/ParserMain.cpp
@@ -13,7 +13,7 @@ public:
     int getNumMasters() const noexcept { return numMasters; }
     int getNumCurves() const noexcept { return numCurves; }
 protected:
-    void callback(std::string_view header, std::vector<sfz::Opcode> members [[maybe_unused]]) final
+    void callback(std::string_view header, const std::vector<sfz::Opcode>& members [[maybe_unused]]) final
     {
         switch (hash(header))
         {
diff --git a/sources/Synth.cpp b/sources/Synth.cpp
index d4ad9965..5f7b48a9 100644
--- a/sources/Synth.cpp
+++ b/sources/Synth.cpp
@@ -4,14 +4,14 @@
 #include <utility>
 #include <algorithm>
 
-void sfz::Synth::callback(std::string_view header, std::vector<Opcode> members)
+void sfz::Synth::callback(std::string_view header, const std::vector<Opcode>& members)
 {
     switch (hash(header))
     {
     case hash("global"):
         // We shouldn't have multiple global headers in file
         ASSERT(!hasGlobal);
-        globalOpcodes = std::move(members);
+        globalOpcodes = members;
         hasGlobal = true;
         break;
     case hash("control"):
@@ -20,11 +20,11 @@ void sfz::Synth::callback(std::string_view header, std::vector<Opcode> members)
         hasControl = true;
         break;
     case hash("master"):
-        masterOpcodes = std::move(members);
+        masterOpcodes = members;
         numMasters++;
         break;
     case hash("group"): 
-        groupOpcodes = std::move(members);
+        groupOpcodes = members;
         numGroups++;
         break;
     case hash("region"):
diff --git a/sources/Synth.h b/sources/Synth.h
index f66100e5..1bc9b6b4 100644
--- a/sources/Synth.h
+++ b/sources/Synth.h
@@ -129,7 +129,7 @@ public:
     void tempo(int delay, float secondsPerQuarter);
 
 protected:
-    void callback(std::string_view header, std::vector<Opcode> members) final;
+    void callback(std::string_view header, const std::vector<Opcode>&  members) final;
 
 private:
     Voice* findFreeVoice()