diff --git a/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerRequest.Managed.cs b/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerRequest.Managed.cs
index 098782eec22151..840b0d8fc6205e 100644
--- a/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerRequest.Managed.cs
+++ b/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerRequest.Managed.cs
@@ -208,15 +208,15 @@ internal void FinishInitialization()
         internal void AddHeader(string header)
         {
             int colon = header.IndexOf(':');
-            if (colon == -1 || colon == 0)
+            if (colon <= 0)
             {
                 _context.ErrorMessage = HttpStatusDescription.Get(400);
                 _context.ErrorStatus = 400;
                 return;
             }
 
-            string name = header.AsSpan(0, colon).Trim().ToString();
-            string val = header.AsSpan(colon + 1).Trim().ToString();
+            string name = header.AsSpan(0, colon).ToString();
+            string val = header.AsSpan(colon + 1).Trim(" \t").ToString();
             if (name.Equals("content-length", StringComparison.OrdinalIgnoreCase))
             {
                 // To match Windows behavior:
diff --git a/src/libraries/System.Net.HttpListener/tests/InvalidClientRequestTests.cs b/src/libraries/System.Net.HttpListener/tests/InvalidClientRequestTests.cs
index 67e7c187225fba..00c52e667a1fb9 100644
--- a/src/libraries/System.Net.HttpListener/tests/InvalidClientRequestTests.cs
+++ b/src/libraries/System.Net.HttpListener/tests/InvalidClientRequestTests.cs
@@ -84,6 +84,13 @@ public static IEnumerable<object[]> InvalidRequest_TestData()
             yield return new object[] { "GET {path} HTTP/1.1", null, new string[] { ":" }, null, "Bad Request" };
             yield return new object[] { "GET {path} HTTP/1.1", null, new string[] { "\0:value" }, null, "Bad Request" };
             yield return new object[] { "GET {path} HTTP/1.1", null, new string[] { "value:\0" }, null, "Bad Request" };
+            if (Helpers.IsManagedImplementation)
+            {
+                yield return new object[] { "GET {path} HTTP/1.1", null, new string[] { " Header: value" }, null, "Bad Request" };
+                yield return new object[] { "GET {path} HTTP/1.1", null, new string[] { "\tHeader: value" }, null, "Bad Request" };
+                yield return new object[] { "GET {path} HTTP/1.1", null, new string[] { "Header : value" }, null, "Bad Request" };
+                yield return new object[] { "GET {path} HTTP/1.1", null, new string[] { "Header\t: value" }, null, "Bad Request" };
+            }
 
             yield return new object[] { "GET {path} HTTP/1.1", "", null, null, "Bad Request" };
             yield return new object[] { "GET {path} HTTP/1.1", "Host: \r\n", null, null, "Bad Request" };