diff --git a/rslib/i18n/build.rs b/rslib/i18n/build.rs
index f604c9167..75bc38787 100644
--- a/rslib/i18n/build.rs
+++ b/rslib/i18n/build.rs
@@ -8,7 +8,6 @@ mod python;
 mod typescript;
 mod write_strings;
 
-use std::env;
 use std::path::PathBuf;
 
 use anki_io::create_dir_all;
@@ -32,8 +31,7 @@ fn main() -> Result<()> {
     python::write_py_interface(&modules)?;
 
     // write strings.json file to requested path
-    println!("cargo:rerun-if-env-changed=STRINGS_JSON");
-    if let Ok(path) = env::var("STRINGS_JSON") {
+    if let Some(path) = option_env!("STRINGS_JSON") {
         if !path.is_empty() {
             let path = PathBuf::from(path);
             let meta_json = serde_json::to_string_pretty(&modules).unwrap();
diff --git a/rslib/i18n/python.rs b/rslib/i18n/python.rs
index ca780c041..a564de48d 100644
--- a/rslib/i18n/python.rs
+++ b/rslib/i18n/python.rs
@@ -1,7 +1,6 @@
 // Copyright: Ankitects Pty Ltd and contributors
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
-use std::env;
 use std::fmt::Write;
 use std::path::PathBuf;
 
@@ -21,7 +20,7 @@ pub fn write_py_interface(modules: &[Module]) -> Result<()> {
     render_methods(modules, &mut out);
     render_legacy_enum(modules, &mut out);
 
-    if let Ok(path) = env::var("STRINGS_PY") {
+    if let Some(path) = option_env!("STRINGS_PY") {
         let path = PathBuf::from(path);
         create_dir_all(path.parent().unwrap())?;
         write_file_if_changed(path, out)?;
diff --git a/rslib/i18n/typescript.rs b/rslib/i18n/typescript.rs
index ce30048e2..0f483cb58 100644
--- a/rslib/i18n/typescript.rs
+++ b/rslib/i18n/typescript.rs
@@ -1,7 +1,6 @@
 // Copyright: Ankitects Pty Ltd and contributors
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
-use std::env;
 use std::fmt::Write;
 use std::path::PathBuf;
 
@@ -22,7 +21,7 @@ pub fn write_ts_interface(modules: &[Module]) -> Result<()> {
     render_module_map(modules, &mut ts_out);
     render_methods(modules, &mut ts_out);
 
-    if let Ok(path) = env::var("STRINGS_TS") {
+    if let Some(path) = option_env!("STRINGS_TS") {
         let path = PathBuf::from(path);
         create_dir_all(path.parent().unwrap())?;
         write_file_if_changed(path, ts_out)?;
diff --git a/rslib/io/src/lib.rs b/rslib/io/src/lib.rs
index cb44467e6..0fd85e490 100644
--- a/rslib/io/src/lib.rs
+++ b/rslib/io/src/lib.rs
@@ -335,6 +335,15 @@ pub fn write_file_if_changed(path: impl AsRef<Path>, contents: impl AsRef<[u8]>)
             .map(|existing| existing != contents)
             .unwrap_or(true)
     };
+
+    match std::env::var("CARGO_PKG_NAME") {
+        Ok(pkg) if pkg == "anki_proto" || pkg == "anki_i18n" => {
+            // at comptime for the proto/i18n crates, register implicit output as input
+            println!("cargo:rerun-if-changed={}", path.to_str().unwrap());
+        }
+        _ => {}
+    }
+
     if changed {
         write_file(path, contents)?;
         Ok(true)