diff --git a/Cargo.lock b/Cargo.lock
index 3b92e7fe..2c3ea457 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -952,6 +952,7 @@ dependencies = [
  "deckcraft-text",
  "i_overlay",
  "image",
+ "js-sys",
  "log",
  "serde",
  "serde_json",
diff --git a/crates/engine/Cargo.toml b/crates/engine/Cargo.toml
index 70479e44..9493ddba 100644
--- a/crates/engine/Cargo.toml
+++ b/crates/engine/Cargo.toml
@@ -28,3 +28,7 @@ image = { workspace = true }
 
 [dev-dependencies]
 deckcraft-anim = { workspace = true }
+
+# The browser clock for comment timestamps (wasm has no std::time::SystemTime).
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+js-sys = "0.3"
diff --git a/crates/engine/src/cmd/review.rs b/crates/engine/src/cmd/review.rs
index c3475aa5..c8370688 100644
--- a/crates/engine/src/cmd/review.rs
+++ b/crates/engine/src/cmd/review.rs
@@ -61,20 +61,29 @@ pub fn specs() -> Vec<CommandSpec> {
     ]
 }
 
-fn now() -> String {
+/// Seconds since the Unix epoch: the system clock, or the browser's on wasm (which has no `SystemTime`).
+fn now_secs() -> u64 {
     #[cfg(not(target_arch = "wasm32"))]
     {
-        let secs = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(0);
-        let (y, m, d) = super::design::civil((secs / 86_400) as i64);
-        let t = secs % 86_400;
-        format!("{y:04}-{m:02}-{d:02}T{:02}:{:02}:{:02}Z", t / 3600, t / 60 % 60, t % 60)
+        std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(0)
     }
     #[cfg(target_arch = "wasm32")]
     {
-        String::new()
+        (js_sys::Date::now() / 1000.0).max(0.0) as u64
     }
 }
 
+/// A UTC timestamp as saved on comments: `2026-10-10T13:10:35Z`.
+fn iso_utc(secs: u64) -> String {
+    let (y, m, d) = super::design::civil((secs / 86_400) as i64);
+    let t = secs % 86_400;
+    format!("{y:04}-{m:02}-{d:02}T{:02}:{:02}:{:02}Z", t / 3600, t / 60 % 60, t % 60)
+}
+
+fn now() -> String {
+    iso_utc(now_secs())
+}
+
 fn add(s: &mut Session, p: &Value) -> Result<Value> {
     let text = str_param(p, "text").ok_or_else(|| bad("comment.add", "missing `text`"))?.to_string();
     let author = s.prefs.author.clone();
@@ -330,6 +339,7 @@ fn custom_show(s: &mut Session, p: &Value) -> Result<Value> {
 
 #[cfg(test)]
 mod tests {
+    use super::*;
     use serde_json::json;
 
     use crate::Session;
@@ -376,4 +386,16 @@ mod tests {
         let here = s.execute("comment.next", &json!({})).unwrap();
         assert_eq!(here["text"], "on first");
     }
+
+    #[test]
+    fn timestamps_are_iso_utc() {
+        assert_eq!(iso_utc(0), "1970-01-01T00:00:00Z");
+        assert_eq!(iso_utc(1_791_637_835), "2026-10-10T13:10:35Z");
+    }
+
+    #[test]
+    fn the_clock_is_not_empty() {
+        // On wasm this used to return an empty string, so browser comments were saved undated.
+        assert!(now().starts_with("20"), "{}", now());
+    }
 }