diff --git a/compiler/gen_dev/src/generic64/aarch64.rs b/compiler/gen_dev/src/generic64/aarch64.rs
index 3410b0fb20..caa675617c 100644
--- a/compiler/gen_dev/src/generic64/aarch64.rs
+++ b/compiler/gen_dev/src/generic64/aarch64.rs
@@ -297,10 +297,6 @@ impl CallConv<AArch64GeneralReg, AArch64FloatReg, AArch64Assembler> for AArch64C
     ) {
         todo!("Loading returned complex symbols for AArch64");
     }
-
-    fn returns_via_arg_pointer(_ret_layout: &Layout) -> bool {
-        todo!("Returning via arg pointer for AArch64");
-    }
 }
 
 impl Assembler<AArch64GeneralReg, AArch64FloatReg> for AArch64Assembler {
diff --git a/compiler/gen_dev/src/generic64/mod.rs b/compiler/gen_dev/src/generic64/mod.rs
index 66f7aa012c..7b31f0178f 100644
--- a/compiler/gen_dev/src/generic64/mod.rs
+++ b/compiler/gen_dev/src/generic64/mod.rs
@@ -107,9 +107,6 @@ pub trait CallConv<GeneralReg: RegTrait, FloatReg: RegTrait, ASM: Assembler<Gene
         sym: &Symbol,
         layout: &Layout<'a>,
     );
-
-    // returns true if the layout should be returned via an argument pointer.
-    fn returns_via_arg_pointer(ret_layout: &Layout) -> bool;
 }
 
 /// Assembler contains calls to the backend assembly generator.
diff --git a/compiler/gen_dev/src/generic64/x86_64.rs b/compiler/gen_dev/src/generic64/x86_64.rs
index 711f42da8f..2286cbd7fc 100644
--- a/compiler/gen_dev/src/generic64/x86_64.rs
+++ b/compiler/gen_dev/src/generic64/x86_64.rs
@@ -496,9 +496,11 @@ impl CallConv<X86_64GeneralReg, X86_64FloatReg, X86_64Assembler> for X86_64Syste
             x => todo!("receiving complex return type, {:?}", x),
         }
     }
+}
 
+impl X86_64SystemV {
     fn returns_via_arg_pointer(ret_layout: &Layout) -> bool {
-        // TODO: This may need to be more complex/extended to fully support the calling convention.
+        // TODO: This will need to be more complex/extended to fully support the calling convention.
         // details here: https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-1.0.pdf
         ret_layout.stack_size(TARGET_INFO) > 16
     }
@@ -840,7 +842,9 @@ impl CallConv<X86_64GeneralReg, X86_64FloatReg, X86_64Assembler> for X86_64Windo
     ) {
         todo!("Loading returned complex symbols for X86_64");
     }
+}
 
+impl X86_64WindowsFastcall {
     fn returns_via_arg_pointer(ret_layout: &Layout) -> bool {
         // TODO: This is not fully correct there are some exceptions for "vector" types.
         // details here: https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=msvc-160#return-values