diff --git a/src/vm/include/Compiler.h b/src/vm/include/Compiler.h
index d272163..1d553ce 100644
--- a/src/vm/include/Compiler.h
+++ b/src/vm/include/Compiler.h
@@ -10,10 +10,10 @@
 
 class Compiler {
 public:
-    static Handle compile(Handle src, Handle fake_env = nullptr, Handle suffix = nullptr);
+    static Handle compile(const Handle &src, Handle fake_env = nullptr, const Handle &suffix = nullptr);
 
 private:
-    static Handle findIndex(Handle symbol, Handle env);
+    static Handle findIndex(const Handle &symbol, const Handle &env);
 };
 
 
diff --git a/src/vm/src/Compiler.cpp b/src/vm/src/Compiler.cpp
index 4b95ef4..9661f75 100644
--- a/src/vm/src/Compiler.cpp
+++ b/src/vm/src/Compiler.cpp
@@ -11,7 +11,7 @@
 
 using namespace Command;
 
-Handle Compiler::compile(Handle src, Handle fake_env, Handle suffix) {
+Handle Compiler::compile(const Handle &src, Handle fake_env, const Handle &suffix) {
     Handle out;
 
     std::function<Handle(Handle)> compileArgsRaw = [&](Handle args) {
@@ -119,7 +119,7 @@ Handle Compiler::compile(Handle src, Handle fake_env, Handle suffix) {
     out.splice(suffix);
     return out;
 }
-Handle Compiler::findIndex(Handle symbol, Handle env) {
+Handle Compiler::findIndex(const Handle &symbol, const Handle &env) {
     int64_t frame = 1;
 
     Handle curFrame = env;