diff --git a/nac3artiq/src/lib.rs b/nac3artiq/src/lib.rs
index a9d8fa1d3..ca2f2f152 100644
--- a/nac3artiq/src/lib.rs
+++ b/nac3artiq/src/lib.rs
@@ -1085,7 +1085,7 @@ impl Nac3 {
         let working_directory = tempfile::Builder::new().prefix("nac3-").tempdir().unwrap();
         fs::write(working_directory.path().join("kernel.ld"), include_bytes!("kernel.ld")).unwrap();
 
-        let mut string_store: HashMap<String, i32> = Default::default();
+        let mut string_store: HashMap<String, i32> = HashMap::default();
 
         // Keep this list of exceptions in sync with `EXCEPTION_ID_LOOKUP` in `artiq::firmware::ksupport::eh_artiq`
         // The exceptions declared here must be defined in `artiq.coredevice.exceptions`
@@ -1120,10 +1120,11 @@ impl Nac3 {
             let exn_name = if name.find(':').is_none() {
                 format!("0:artiq.coredevice.exceptions.{name}")
             } else {
-                name.to_string()
+                (*name).to_string()
             };
 
-            string_store.insert(exn_name, i as i32);
+            let id = i32::try_from(i).unwrap();
+            string_store.insert(exn_name, id);
         }
 
         Ok(Nac3 {
diff --git a/nac3artiq/src/symbol_resolver.rs b/nac3artiq/src/symbol_resolver.rs
index fa57755dc..f4509fe1c 100644
--- a/nac3artiq/src/symbol_resolver.rs
+++ b/nac3artiq/src/symbol_resolver.rs
@@ -1536,7 +1536,7 @@ impl SymbolResolver for Resolver {
         if let Some(id) = string_store.get(s) {
             *id
         } else {
-            let id = string_store.len() as i32;
+            let id = i32::try_from(string_store.len()).unwrap();
             string_store.insert(s.into(), id);
             id
         }