diff --git a/core/src/avm2/globals/flash/utils/Timer.as b/core/src/avm2/globals/flash/utils/Timer.as
index c53e78b16..c17b8b0ee 100644
--- a/core/src/avm2/globals/flash/utils/Timer.as
+++ b/core/src/avm2/globals/flash/utils/Timer.as
@@ -32,11 +32,12 @@ package flash.utils {
 			this.checkDelay(delay);
 			this._delay = value;
 			if (this.running) {
-				this.stop();
-				this.start();
+				this.updateDelay();
 			}
 		}
 
+		private native function updateDelay():void;
+
 		public function get repeatCount(): int {
 			return this._repeatCount;
 		}
diff --git a/core/src/avm2/globals/flash/utils/timer.rs b/core/src/avm2/globals/flash/utils/timer.rs
index 496af0f33..196d1ca95 100644
--- a/core/src/avm2/globals/flash/utils/timer.rs
+++ b/core/src/avm2/globals/flash/utils/timer.rs
@@ -81,3 +81,32 @@ pub fn start<'gc>(
     }
     Ok(Value::Undefined)
 }
+
+/// Implements `Timer.updateDelay`
+pub fn update_delay<'gc>(
+    activation: &mut Activation<'_, 'gc>,
+    this: Object<'gc>,
+    _args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error<'gc>> {
+    let id = this
+        .get_property(
+            &Multiname::new(activation.avm2().flash_utils_internal, "_timerId"),
+            activation,
+        )
+        .unwrap()
+        .coerce_to_i32(activation)?;
+
+    let delay = this
+        .get_property(
+            &Multiname::new(activation.avm2().flash_utils_internal, "_delay"),
+            activation,
+        )
+        .unwrap()
+        .coerce_to_i32(activation)?;
+
+    if id != -1 {
+        activation.context.timers.set_delay(id, delay);
+    }
+
+    Ok(Value::Undefined)
+}
diff --git a/core/src/timer.rs b/core/src/timer.rs
index f10f6c219..7fb5fff34 100644
--- a/core/src/timer.rs
+++ b/core/src/timer.rs
@@ -258,6 +258,29 @@ impl<'gc> Timers<'gc> {
         len < old_len
     }
 
+    /// Changes the delay of a timer.
+    pub fn set_delay(&mut self, id: i32, interval: i32) {
+        // SANITY: Set a minimum interval so we don't spam too much.
+        let interval = interval.max(Self::MIN_INTERVAL) as u64 * (Self::TIMER_SCALE as u64);
+
+        // Due to the limitations of `BinaryHeap`, we have to do this in a slightly roundabout way.
+        let mut timer = None;
+        for t in self.timers.iter() {
+            if t.id == id {
+                timer = Some(t.clone());
+                break;
+            }
+        }
+
+        if let Some(mut timer) = timer {
+            self.remove(id);
+            timer.interval = interval;
+            self.timers.push(timer);
+        } else {
+            panic!("Changing delay of non-existent timer");
+        }
+    }
+
     fn peek(&self) -> Option<&Timer<'gc>> {
         self.timers.peek()
     }
@@ -286,7 +309,7 @@ unsafe impl<'gc> Collect for Timers<'gc> {
 }
 /// A timer created via `setInterval`/`setTimeout`.
 /// Runs a callback when it ticks.
-#[derive(Collect)]
+#[derive(Clone, Collect)]
 #[collect(no_drop)]
 pub struct Timer<'gc> {
     /// The ID of the timer.