diff --git a/src/Scope.cc b/src/Scope.cc
index 24e3b87f62..d4a2d5f1b5 100644
--- a/src/Scope.cc
+++ b/src/Scope.cc
@@ -197,7 +197,7 @@ void merge_top_scope()
 
 	auto t = pop_scope();
 
-	for ( auto v : t->OrderedVars() )
+	for ( const auto& v : t->OrderedVars() )
 		{
 		v->SetOffset(top_scope->Length());
 		top_scope->Insert(v->Name(), v);
diff --git a/src/script_opt/CPP/Driver.cc b/src/script_opt/CPP/Driver.cc
index aae5ffe321..09e9205685 100644
--- a/src/script_opt/CPP/Driver.cc
+++ b/src/script_opt/CPP/Driver.cc
@@ -453,7 +453,7 @@ void CPPCompile::GenFinishInit()
 
 	NL();
 	int max_cohort = 0;
-	for ( auto gi : all_global_info )
+	for ( const auto& gi : all_global_info )
 		max_cohort = std::max(max_cohort, gi->MaxCohort());
 
 	for ( auto c = 0; c <= max_cohort; ++c )
diff --git a/src/script_opt/CPP/Inits.cc b/src/script_opt/CPP/Inits.cc
index 171350b83a..9845e70363 100644
--- a/src/script_opt/CPP/Inits.cc
+++ b/src/script_opt/CPP/Inits.cc
@@ -196,7 +196,7 @@ void CPPCompile::InitializeGlobals()
 	Emit("Frame* f__CPP = nullptr;");
 	NL();
 
-	for ( auto ginit : IDOptInfo::GetGlobalInitExprs() )
+	for ( const auto& ginit : IDOptInfo::GetGlobalInitExprs() )
 		{
 		auto g = ginit.Id();
 		if ( pfs.Globals().count(g) == 0 )