diff --git a/Cargo.lock b/Cargo.lock
index 70c55dcc1..7572443f1 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -354,6 +354,7 @@ dependencies = [
  "calyx-frontend",
  "calyx-ir",
  "calyx-utils",
+ "interp",
  "proc-macro2",
  "quote",
  "syn 2.0.87",
diff --git a/tools/calyx-ffi-macro/Cargo.toml b/tools/calyx-ffi-macro/Cargo.toml
index e9d1eddc1..88d8b42af 100644
--- a/tools/calyx-ffi-macro/Cargo.toml
+++ b/tools/calyx-ffi-macro/Cargo.toml
@@ -18,7 +18,7 @@ proc-macro = true
 proc-macro2 = "1.0.86"
 quote = "1.0.36"
 syn = { version = "2.0.69", features = ["full", "visit"] }
+interp = { path = "../../interp" }
 calyx-utils.workspace = true
 calyx-frontend.workspace = true
 calyx-ir.workspace = true
-# bigint = "4.4.3"
diff --git a/tools/calyx-ffi-macro/src/calyx.rs b/tools/calyx-ffi-macro/src/calyx.rs
index 403932197..73490bfd2 100644
--- a/tools/calyx-ffi-macro/src/calyx.rs
+++ b/tools/calyx-ffi-macro/src/calyx.rs
@@ -19,7 +19,7 @@ pub fn parse_calyx_file(
     args: &CalyxFFIMacroArgs,
     file: PathBuf,
 ) -> Result<CalyxComponent, TokenStream> {
-    // there has to be a better way to find lib
+    // TODO(ethan): there has to be a better way to find lib
     let home_dir = env::var("HOME").expect("user home not set");
     let mut lib_path = PathBuf::from(home_dir);
     lib_path.push(".calyx");
diff --git a/tools/calyx-ffi-macro/src/lib.rs b/tools/calyx-ffi-macro/src/lib.rs
index a6329225d..ac7a0bb02 100644
--- a/tools/calyx-ffi-macro/src/lib.rs
+++ b/tools/calyx-ffi-macro/src/lib.rs
@@ -11,9 +11,6 @@ mod calyx;
 mod parse;
 mod util;
 
-// this is super bad, might go out of sync with interp::WidthInt
-type WidthInt = u32;
-
 /// Connects this `struct` to a calyx component in the given file.
 #[proc_macro_attribute]
 pub fn calyx_ffi(attrs: TokenStream, item: TokenStream) -> TokenStream {
@@ -66,7 +63,7 @@ pub fn calyx_ffi(attrs: TokenStream, item: TokenStream) -> TokenStream {
 
         port_names.push(port_name.clone());
 
-        let port_width = port.borrow().width as WidthInt;
+        let port_width = port.borrow().width as interp::WidthInt;
         let width_getter = format_ident!("{}_width", port_name);
         width_getters.push(quote! {
             pub const fn #width_getter() -> calyx_ffi::value::WidthInt {