diff --git a/webcodecs/audio-data.any.js b/webcodecs/audio-data.any.js
index d5d950647767bc4..67fef3c83c858f2 100644
--- a/webcodecs/audio-data.any.js
+++ b/webcodecs/audio-data.any.js
@@ -192,6 +192,7 @@ const TEST_TEMPLATE = {
   // For each test, copy this template and replace the number by the appropriate
   // number for this type
   testInput: [MIN, BIAS, MAX, MIN, HALF, NEGATIVE_HALF, BIAS, MAX, BIAS, BIAS],
+  testInterleavedResult: [MIN, NEGATIVE_HALF, BIAS, BIAS, MAX, MAX, MIN, BIAS, HALF, BIAS],
   testVectorInterleavedResult: [
     [MIN, MAX, HALF, BIAS, BIAS],
     [BIAS, MIN, NEGATIVE_HALF, MAX, BIAS],
@@ -274,6 +275,10 @@ function get_type_values(type) {
     cloned.testInput,
     idx => TEST_VALUES[type][idx]
   );
+  cloned.testInterleavedResult = Array.from(
+    cloned.testInterleavedResult,
+    idx => TEST_VALUES[type][idx]
+  );
   cloned.testVectorInterleavedResult = Array.from(
     cloned.testVectorInterleavedResult,
     c => {
@@ -418,7 +423,15 @@ function conversionTest(sourceType, destinationType) {
       "planar channel 1",
       assert_func
     );
-    // Planar to interleaved isn't supported
+    // Copy to interleaved from planar: all channels are copied
+    data.copyTo(destInterleaved, {planeIndex: 0, format: destinationType});
+    check_array_equality(
+      destInterleaved,
+      result.testInterleavedResult,
+      sourceType,
+      "planar to interleaved",
+      assert_func
+    );
   }, `Test conversion of ${sourceType} to ${destinationType}`);
 }