diff --git a/Cargo.lock b/Cargo.lock
index d2378c2f5..e641364be 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -274,6 +274,7 @@ dependencies = [
 name = "archives"
 version = "0.0.0"
 dependencies = [
+ "anki_io",
  "camino",
  "flate2",
  "reqwest",
diff --git a/build/archives/Cargo.toml b/build/archives/Cargo.toml
index 3092134d4..05e6a1dce 100644
--- a/build/archives/Cargo.toml
+++ b/build/archives/Cargo.toml
@@ -9,6 +9,7 @@ license.workspace = true
 rust-version.workspace = true
 
 [dependencies]
+anki_io = { version = "0.0.0", path = "../../rslib/io" }
 camino = "1.1.4"
 flate2 = "1.0.25"
 sha2 = { version = "0.10.6" }
diff --git a/build/archives/src/main.rs b/build/archives/src/main.rs
index ddb74011c..3f6b4c724 100644
--- a/build/archives/src/main.rs
+++ b/build/archives/src/main.rs
@@ -4,7 +4,9 @@
 use std::error::Error;
 use std::fs;
 use std::io::Read;
+use std::path::Path;
 
+use anki_io::read_file;
 use camino::Utf8Path;
 use sha2::Digest;
 
@@ -19,7 +21,7 @@ async fn main() -> Result<()> {
         "download" => {
             let archive_url = &args[2];
             let checksum = &args[3];
-            let output_path = &args[4];
+            let output_path = Path::new(&args[4]);
             download_and_check(archive_url, checksum, output_path).await?;
         }
         "extract" => {
@@ -33,13 +35,15 @@ async fn main() -> Result<()> {
     Ok(())
 }
 
-async fn download_and_check(archive_url: &str, checksum: &str, output_path: &str) -> Result<()> {
+async fn download_and_check(archive_url: &str, checksum: &str, output_path: &Path) -> Result<()> {
+    // skip download if we already have a valid file
+    if output_path.exists() && sha2_data(&read_file(output_path)?) == checksum {
+        return Ok(());
+    }
+
     let response = reqwest::get(archive_url).await?.error_for_status()?;
     let data = response.bytes().await?.to_vec();
-    let mut digest = sha2::Sha256::new();
-    digest.update(&data);
-    let result = digest.finalize();
-    let actual_checksum = format!("{:x}", result);
+    let actual_checksum = sha2_data(&data);
     if actual_checksum != checksum {
         println!("expected {checksum}, got {actual_checksum}");
         std::process::exit(1);
@@ -49,6 +53,13 @@ async fn download_and_check(archive_url: &str, checksum: &str, output_path: &str
     Ok(())
 }
 
+fn sha2_data(data: &[u8]) -> String {
+    let mut digest = sha2::Sha256::new();
+    digest.update(data);
+    let result = digest.finalize();
+    format!("{:x}", result)
+}
+
 enum CompressionKind {
     Zstd,
     Gzip,
diff --git a/build/ninja_gen/src/archives.rs b/build/ninja_gen/src/archives.rs
index 70b40e797..075c22e81 100644
--- a/build/ninja_gen/src/archives.rs
+++ b/build/ninja_gen/src/archives.rs
@@ -97,6 +97,10 @@ impl BuildAction for DownloadArchive {
     fn on_first_instance(&self, build: &mut Build) -> Result<()> {
         build_archive_tool(build)
     }
+
+    fn check_output_timestamps(&self) -> bool {
+        true
+    }
 }
 
 struct ExtractArchive<'a, I> {
@@ -155,6 +159,10 @@ where
     fn name(&self) -> &'static str {
         "extract"
     }
+
+    fn check_output_timestamps(&self) -> bool {
+        true
+    }
 }
 
 fn build_archive_tool(build: &mut Build) -> Result<()> {