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diff --git a/testing/web-platform/tests/webaudio/the-audio-api/the-audioparam-interface/retrospective-setTargetAtTime.html b/testing/web-platform/tests/webaudio/the-audio-api/the-audioparam-interface/retrospective-setTargetAtTime.html
new file mode 100644
index 0000000000..41a37bdb91
--- /dev/null
+++ b/testing/web-platform/tests/webaudio/the-audio-api/the-audioparam-interface/retrospective-setTargetAtTime.html
@@ -0,0 +1,80 @@
+<!doctype html>
+<meta charset=utf-8>
+<html>
+  <head>
+    <title>Test setTargetAtTime with start time in the past</title>
+    <script src=/resources/testharness.js></script>
+    <script src=/resources/testharnessreport.js></script>
+    <script src="/webaudio/resources/audit-util.js"></script>
+    <script src="/webaudio/resources/audit.js"></script>
+  </head>
+  <body>
+    <script>
+      let audit = Audit.createTaskRunner();
+
+      audit.define(
+          {
+            label: 'test',
+            description: 'Test setTargetAtTime with start time in the past'
+          },
+          (task, should) => {
+            // Use a sample rate that is a power of two to eliminate round-off
+            // in computing the currentTime.
+            let context = new OfflineAudioContext(2, 16384, 16384);
+            let source = new ConstantSourceNode(context);
+
+            // Suspend the context at this frame so we can synchronously set up
+            // automations.
+            const suspendFrame = 128;
+
+            let test = new GainNode(context);
+            let reference = new GainNode(context);
+
+            source.connect(test);
+            source.connect(reference);
+
+            let merger = new ChannelMergerNode(
+                context, {numberOfInputs: context.destination.channelCount});
+            test.connect(merger, 0, 0);
+            reference.connect(merger, 0, 1);
+
+            merger.connect(context.destination);
+
+            context.suspend(suspendFrame / context.sampleRate)
+                .then(() => {
+                  // Call setTargetAtTime with a time in the past
+                  test.gain.setTargetAtTime(0.1, 0.5*context.currentTime, 0.1);
+                  reference.gain.setTargetAtTime(0.1, context.currentTime, 0.1);
+                })
+                .then(() => context.resume());
+
+            source.start();
+
+            context.startRendering()
+                .then(resultBuffer => {
+                  let testValue = resultBuffer.getChannelData(0);
+                  let referenceValue = resultBuffer.getChannelData(1);
+
+                  // Until the suspendFrame, both should be exactly equal to 1.
+                  should(
+                      testValue.slice(0, suspendFrame),
+                      `Test[0:${suspendFrame - 1}]`)
+                      .beConstantValueOf(1);
+                  should(
+                      referenceValue.slice(0, suspendFrame),
+                      `Reference[0:${suspendFrame - 1}]`)
+                      .beConstantValueOf(1);
+
+                  // After the suspendFrame, both should be equal (and not
+                  // constant)
+                  should(
+                      testValue.slice(suspendFrame), `Test[${suspendFrame}:]`)
+                      .beEqualToArray(referenceValue.slice(suspendFrame));
+                })
+                .then(() => task.done());
+          });
+
+      audit.run();
+    </script>
+  </body>
+</html>