diff --git a/pkgs/http/CHANGELOG.md b/pkgs/http/CHANGELOG.md
index 5ff32e430f..8b56ac48d5 100644
--- a/pkgs/http/CHANGELOG.md
+++ b/pkgs/http/CHANGELOG.md
@@ -8,6 +8,11 @@
 * Preserve header cases in `IOClient`.
 * Fix a [bug](https://github.com/dart-lang/http/issues/1934) to release the
   underlying connection when an `AbortableRequest` is aborted before its body is read.
+* Stop `IOClient` from sending bodyless GET/HEAD requests with
+  `Transfer-Encoding: chunked` when `BaseRequest.contentLength` is `null`;
+  `dart:io`'s per-method default framing is used instead. A GET or HEAD request
+  that streams a non-empty body while leaving `contentLength` `null` now throws
+  instead of being sent chunked.
 
 ## 1.6.0
 
diff --git a/pkgs/http/lib/src/io_client.dart b/pkgs/http/lib/src/io_client.dart
index a00ef9dd03..dc32f23b83 100644
--- a/pkgs/http/lib/src/io_client.dart
+++ b/pkgs/http/lib/src/io_client.dart
@@ -114,8 +114,10 @@ class IOClient extends BaseClient {
       var ioRequest = (await _inner!.openUrl(request.method, request.url))
         ..followRedirects = request.followRedirects
         ..maxRedirects = request.maxRedirects
-        ..contentLength = (request.contentLength ?? -1)
         ..persistentConnection = request.persistentConnection;
+      if (request.contentLength case final contentLength?) {
+        ioRequest.contentLength = contentLength;
+      }
       request.headers.forEach((name, value) {
         ioRequest.headers.set(name, value, preserveHeaderCase: true);
       });
diff --git a/pkgs/http/test/io/streamed_request_test.dart b/pkgs/http/test/io/streamed_request_test.dart
index f0e990c767..c39437c2bc 100644
--- a/pkgs/http/test/io/streamed_request_test.dart
+++ b/pkgs/http/test/io/streamed_request_test.dart
@@ -40,6 +40,19 @@ void main() {
       expect(await utf8.decodeStream(response.stream),
           parse(containsPair('headers', isNot(contains('content-length')))));
     });
+
+    test('defaults to sending a bodyless GET without framing headers',
+        () async {
+      var request = http.StreamedRequest('GET', serverUrl);
+      unawaited(request.sink.close());
+      var response = await request.send();
+      expect(
+          await utf8.decodeStream(response.stream),
+          parse(containsPair(
+              'headers',
+              allOf(isNot(contains('transfer-encoding')),
+                  isNot(contains('content-length'))))));
+    });
   });
 
   // Regression test.