diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3bda5bfdaac..1f6ecc4d90e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,14 @@
 
 ### Libraries
 
+#### `dart:io`
+
+- **Breaking change** [#53005][]: The headers returned by
+  `HttpClientResponse.headers` and `HttpRequest.headers` no longer include
+  trailing whitespace in their values.
+
+[#52334]: https://dartbug.com/53005
+
 #### `dart:js_interop`
 
 - **JSNumber.toDart and Object.toJS**:
diff --git a/sdk/lib/_http/http_parser.dart b/sdk/lib/_http/http_parser.dart
index 0a8bba4c042..9ea44e75a48 100644
--- a/sdk/lib/_http/http_parser.dart
+++ b/sdk/lib/_http/http_parser.dart
@@ -683,6 +683,9 @@ class _HttpParser extends Stream<_HttpIncoming> {
             _state = _State.HEADER_VALUE_START;
           } else {
             String headerField = String.fromCharCodes(_headerField);
+            // The field value does not include any leading or trailing whitespace.
+            // See https://www.rfc-editor.org/rfc/rfc7230#section-3.2.4
+            _removeTrailingSpaces(_headerValue);
             String headerValue = String.fromCharCodes(_headerValue);
             const errorIfBothText = "Both Content-Length and Transfer-Encoding "
                 "are specified, at most one is allowed";
@@ -1002,6 +1005,17 @@ class _HttpParser extends Stream<_HttpIncoming> {
     return (byte > 31 && byte < 128) || (byte == _CharCode.HT);
   }
 
+  static void _removeTrailingSpaces(List<int> value) {
+    var length = value.length;
+    while (length > 0 &&
+        (value[length - 1] == _CharCode.SP ||
+            value[length - 1] == _CharCode.HT)) {
+      --length;
+    }
+
+    value.length = length;
+  }
+
   static List<String> _tokenizeFieldValue(String headerValue) {
     List<String> tokens = <String>[];
     int start = 0;
diff --git a/tests/standalone/io/http_parser_test.dart b/tests/standalone/io/http_parser_test.dart
index af618a4ebac..af375beb399 100644
--- a/tests/standalone/io/http_parser_test.dart
+++ b/tests/standalone/io/http_parser_test.dart
@@ -381,13 +381,24 @@ POST /test HTTP/1.1\r
 
     request = """
 POST /test HTTP/1.1\r
-Header-A: AAA\r
-X-Header-B: bbb\r
+Header-A: AAA  aaa\r
+X-Header-B: bbb  BBB\r
 \r
 """;
     headers = new Map();
-    headers["header-a"] = "AAA";
-    headers["x-header-b"] = "bbb";
+    headers["header-a"] = "AAA  aaa";
+    headers["x-header-b"] = "bbb  BBB";
+    _testParseRequestLean(request, "POST", "/test", expectedHeaders: headers);
+
+    request = """
+POST /test HTTP/1.1\r
+Header-A:   \t AAA  aaa \t \r
+X-Header-B:   \t bbb  BBB  \t \r
+\r
+""";
+    headers = new Map();
+    headers["header-a"] = "AAA  aaa";
+    headers["x-header-b"] = "bbb  BBB";
     _testParseRequestLean(request, "POST", "/test", expectedHeaders: headers);
 
     request = """
@@ -404,22 +415,23 @@ Empty-Header-2:\r
 
     request = """
 POST /test HTTP/1.1\r
-Header-A:   AAA\r
-X-Header-B:\t \t bbb\r
+Empty-Header-1:\t  \t \r
+Empty-Header-2:\t  \t \r
+        \r
 \r
 """;
     headers = new Map();
-    headers["header-a"] = "AAA";
-    headers["x-header-b"] = "bbb";
+    headers["empty-header-1"] = "";
+    headers["empty-header-2"] = "";
     _testParseRequestLean(request, "POST", "/test", expectedHeaders: headers);
 
     request = """
 POST /test HTTP/1.1\r
-Header-A:   AA\r
- A\r
+Header-A: \t  AA\r
+ A  \t \r
 X-Header-B:           b\r
   b\r
-\t    b\r
+\t    b  \t \r
 \r
 """;
 
@@ -461,6 +473,19 @@ Transfer-Encoding: chunked\r
 01234\r
 5\r
 56789\r
+0\r\n\r\n""";
+    _testParseRequest(request, "POST", "/test",
+        expectedTransferLength: -1, expectedBytesReceived: 10, chunked: true);
+
+    // Test LWS around chunked encoding header value.
+    request = """
+POST /test HTTP/1.1\r
+Transfer-Encoding:   \t   chunked  \t \r
+\r
+5\r
+01234\r
+5\r
+56789\r
 0\r\n\r\n""";
     _testParseRequest(request, "POST", "/test",
         expectedTransferLength: -1, expectedBytesReceived: 10, chunked: true);
@@ -569,6 +594,10 @@ Sec-WebSocket-Version: 13\r
     _testParseResponse(response, 100, "Continue",
         expectedTransferLength: 10, expectedBytesReceived: 0);
 
+    response = "HTTP/1.1 100 Continue\r\nContent-Length: \t  10 \t \r\n\r\n";
+    _testParseResponse(response, 100, "Continue",
+        expectedTransferLength: 10, expectedBytesReceived: 0);
+
     response = "HTTP/1.1 200 OK\r\nContent-Length: 0\r\n"
         "Connection: Close\r\n\r\n";
     _testParseResponse(response, 200, "OK", connectionClose: true);