@@ -1083,14 +1083,25 @@ function pipeToSync(source, ...args) {
     }
   } catch (error) {
     if (!options.preventFail) {
-      writer.fail?.(error);
+      failWriterQuietly(writer, error);
     }
     throw error;
   }
 
   return totalBytes;
 }
 
+// Call writer.fail(error) on a best-effort basis. The error that made the
+// pipe fail is what the caller must see; an exception from fail() itself
+// must not replace it.
+function failWriterQuietly(writer, error) {
+  try {
+    writer.fail?.(error);
+  } catch {
+    // Ignored, see above.
+  }
+}
+
 /**
  * Write an async source through transforms to a writer.
  * @param {AsyncIterable<Uint8Array[]>|Iterable<Uint8Array[]>} source
@@ -1108,7 +1119,7 @@ async function pipeTo(source, ...args) {
 
   function failWriter(error) {
     if (!options.preventFail) {
-      writer.fail?.(error);
+      failWriterQuietly(writer, error);
     }
   }
 
 
@@ -5,7 +5,7 @@
 
 const common = require('../common');
 const assert = require('assert');
-const { pipeToSync, fromSync } = require('stream/iter');
+const { pipeTo, pipeToSync, fromSync } = require('stream/iter');
 
 // pipeToSync cannot complete when endSync() requires async fallback.
 async function testPipeToSyncEndSyncFailure() {
@@ -68,9 +68,46 @@ async function testPipeToSyncPreventClose() {
   assert.strictEqual(endCalled, false);
 }
 
+// An exception thrown by writer.fail() must not replace the error that made
+// the pipe fail.
+async function testFailThrowingDoesNotMaskError() {
+  const cause = new Error('write failed');
+  const syncWriter = {
+    writeSync() { throw cause; },
+    endSync: common.mustNotCall(),
+    fail: common.mustCall((error) => {
+      assert.strictEqual(error, cause);
+      throw new Error('fail() threw');
+    }),
+  };
+  assert.throws(() => pipeToSync(fromSync('data'), syncWriter),
+                (error) => error === cause);
+
+  const asyncWriter = {
+    async write() { throw cause; },
+    end: common.mustNotCall(),
+    fail: common.mustCall((error) => {
+      assert.strictEqual(error, cause);
+      throw new Error('fail() threw');
+    }),
+  };
+  await assert.rejects(pipeTo(fromSync('data'), asyncWriter),
+                       (error) => error === cause);
+
+  // Same for the already-aborted signal path of pipeTo().
+  const signal = AbortSignal.abort();
+  await assert.rejects(
+    pipeTo(fromSync('data'), {
+      write: common.mustNotCall(),
+      fail() { throw new Error('fail() threw'); },
+    }, { signal }),
+    (error) => error === signal.reason);
+}
+
 Promise.all([
   testPipeToSyncEndSyncFailure(),
   testPipeToSyncNoEndSync(),
   testPipeToSyncPreventFail(),
   testPipeToSyncPreventClose(),
+  testFailThrowingDoesNotMaskError(),
 ]).then(common.mustCall());
Original file line number	Diff line number	Diff line change
`@@ -1083,14 +1083,25 @@ function pipeToSync(source, ...args) {`
`1083`	`1083`	`}`
`1084`	`1084`	`} catch (error) {`
`1085`	`1085`	`if (!options.preventFail) {`
`1086`		`- writer.fail?.(error);`
	`1086`	`+ failWriterQuietly(writer, error);`
`1087`	`1087`	`}`
`1088`	`1088`	`throw error;`
`1089`	`1089`	`}`
`1090`	`1090`
`1091`	`1091`	`return totalBytes;`
`1092`	`1092`	`}`
`1093`	`1093`
	`1094`	`+// Call writer.fail(error) on a best-effort basis. The error that made the`
	`1095`	`+// pipe fail is what the caller must see; an exception from fail() itself`
	`1096`	`+// must not replace it.`
	`1097`	`+function failWriterQuietly(writer, error) {`
	`1098`	`+ try {`
	`1099`	`+ writer.fail?.(error);`
	`1100`	`+ } catch {`
	`1101`	`+ // Ignored, see above.`
	`1102`	`+ }`
	`1103`	`+}`
	`1104`	`+`
`1094`	`1105`	`/**`
`1095`	`1106`	`* Write an async source through transforms to a writer.`
`1096`	`1107`	`* @param {AsyncIterable<Uint8Array[]>\|Iterable<Uint8Array[]>} source`
`@@ -1108,7 +1119,7 @@ async function pipeTo(source, ...args) {`
`1108`	`1119`
`1109`	`1120`	`function failWriter(error) {`
`1110`	`1121`	`if (!options.preventFail) {`
`1111`		`- writer.fail?.(error);`
	`1122`	`+ failWriterQuietly(writer, error);`
`1112`	`1123`	`}`
`1113`	`1124`	`}`
`1114`	`1125`