diff --git a/abstio/src/abst_data.rs b/abstio/src/abst_data.rs
index 5012c796e5..f5607050ef 100644
--- a/abstio/src/abst_data.rs
+++ b/abstio/src/abst_data.rs
@@ -16,10 +16,11 @@ pub struct Manifest {
 pub struct Entry {
     /// md5sum of the file
     pub checksum: String,
-    /// Uncompressed size in bytes
-    pub uncompressed_size_bytes: usize,
+    /// Uncompressed size in bytes. Because we have some massive files more than 2^32 bytes
+    /// described by this, explicitly use u64 instead of usize, so wasm doesn't break.
+    pub uncompressed_size_bytes: u64,
     /// Compressed size in bytes
-    pub compressed_size_bytes: usize,
+    pub compressed_size_bytes: u64,
 }
 
 impl Manifest {
diff --git a/map_gui/src/tools/updater.rs b/map_gui/src/tools/updater.rs
index bd32ee78ce..b5972a5979 100644
--- a/map_gui/src/tools/updater.rs
+++ b/map_gui/src/tools/updater.rs
@@ -107,7 +107,7 @@ impl<A: AppLike + 'static> State<A> for Picker<A> {
 }
 
 // For each city, how many total bytes do the runtime files cost to download?
-fn size_per_city(manifest: &Manifest) -> BTreeMap<String, usize> {
+fn size_per_city(manifest: &Manifest) -> BTreeMap<String, u64> {
     let mut per_city = BTreeMap::new();
     for (path, entry) in &manifest.entries {
         let parts = path.split("/").collect::<Vec<_>>();
@@ -122,7 +122,7 @@ fn size_per_city(manifest: &Manifest) -> BTreeMap<String, usize> {
     per_city
 }
 
-fn prettyprint_bytes(bytes: usize) -> String {
+fn prettyprint_bytes(bytes: u64) -> String {
     if bytes < 1024 {
         return format!("{} bytes", bytes);
     }
@@ -220,13 +220,13 @@ pub fn sync_missing_files(timer: &mut Timer) -> Vec<String> {
 }
 
 // Bytes downloaded if succesful
-fn download(url: &str, local_path: String) -> Result<usize> {
+fn download(url: &str, local_path: String) -> Result<u64> {
     let mut resp = reqwest::blocking::get(url)?;
     if !resp.status().is_success() {
         bail!("bad status: {:?}", resp.status());
     }
     let mut buffer: Vec<u8> = Vec::new();
-    let bytes = resp.copy_to(&mut buffer)? as usize;
+    let bytes = resp.copy_to(&mut buffer)?;
 
     info!("Decompressing {} ({})", url, prettyprint_bytes(bytes));
     let mut decoder = flate2::read::GzDecoder::new(&buffer[..]);
diff --git a/updater/src/main.rs b/updater/src/main.rs
index 4a73c6fa01..cf50bf4e63 100644
--- a/updater/src/main.rs
+++ b/updater/src/main.rs
@@ -156,7 +156,7 @@ fn upload(version: String) {
             // generate_manifest.
             entry.compressed_size_bytes = std::fs::metadata(&remote_path)
                 .expect(&format!("Compressed {} not there?", remote_path))
-                .len() as usize;
+                .len();
             (path, entry)
         },
     ) {
@@ -254,7 +254,7 @@ fn generate_manifest() -> Manifest {
 }
 
 /// Returns (checksum, uncompressed_size_bytes)
-fn md5sum(path: &str) -> (String, usize) {
+fn md5sum(path: &str) -> (String, u64) {
     // since these files can be very large, computes the md5 hash in chunks
     let mut file = File::open(path).unwrap();
     let mut buffer = [0 as u8; MD5_BUF_READ_SIZE];
@@ -267,7 +267,10 @@ fn md5sum(path: &str) -> (String, usize) {
         uncompressed_size_bytes += n;
         context.consume(&buffer[..n]);
     }
-    (format!("{:x}", context.compute()), uncompressed_size_bytes)
+    (
+        format!("{:x}", context.compute()),
+        uncompressed_size_bytes as u64,
+    )
 }
 
 fn rm(path: &str) {