diff --git a/reid/src/codegen.rs b/reid/src/codegen.rs
index 29d0bd1..1abfbdc 100644
--- a/reid/src/codegen.rs
+++ b/reid/src/codegen.rs
@@ -367,7 +367,7 @@ impl mir::Module {
                 stack_values.insert(
                     p_name.clone(),
                     StackValue(
-                        StackValueKind::Mutable(alloca),
+                        StackValueKind::mutable(p_ty.is_mutable(), alloca),
                         TypeKind::Ptr(Box::new(p_ty.clone())),
                     ),
                 );
diff --git a/reid/src/mir/impl.rs b/reid/src/mir/impl.rs
index 8e22a07..503b1c7 100644
--- a/reid/src/mir/impl.rs
+++ b/reid/src/mir/impl.rs
@@ -75,8 +75,8 @@ impl TypeKind {
 
     pub fn is_mutable(&self) -> bool {
         match self {
-            TypeKind::Borrow(_, true) => true,
-            _ => false,
+            TypeKind::Borrow(_, false) => false,
+            _ => true,
         }
     }
 }
diff --git a/reid/src/mir/typecheck.rs b/reid/src/mir/typecheck.rs
index d438205..77e83fb 100644
--- a/reid/src/mir/typecheck.rs
+++ b/reid/src/mir/typecheck.rs
@@ -161,8 +161,8 @@ impl FunctionDefinition {
                 .set(
                     param.0.clone(),
                     ScopeVariable {
-                        ty: param_t,
-                        mutable: true,
+                        ty: param_t.clone(),
+                        mutable: param_t.is_mutable(),
                     },
                 )
                 .or(Err(ErrorKind::VariableAlreadyDefined(param.0.clone())));