diff --git a/Tests/HttpUnitTests/HttpUnitTests.nfproj b/Tests/HttpUnitTests/HttpUnitTests.nfproj
index 1ac9eae..efba09e 100644
--- a/Tests/HttpUnitTests/HttpUnitTests.nfproj
+++ b/Tests/HttpUnitTests/HttpUnitTests.nfproj
@@ -35,6 +35,7 @@
     <Compile Include="MockContent.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="UriUnitTests.cs" />
+    <Compile Include="WebHeaderCollectionTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="packages.lock.json" />
diff --git a/Tests/HttpUnitTests/WebHeaderCollectionTests.cs b/Tests/HttpUnitTests/WebHeaderCollectionTests.cs
new file mode 100644
index 0000000..d5d6d91
--- /dev/null
+++ b/Tests/HttpUnitTests/WebHeaderCollectionTests.cs
@@ -0,0 +1,101 @@
+//
+// Copyright (c) .NET Foundation and Contributors
+// See LICENSE file in the project root for full license information.
+//
+
+using nanoFramework.TestFramework;
+using System;
+using System.Net;
+
+namespace HttpUnitTests
+{
+    [TestClass]
+    public class WebHeaderCollectionTests
+    {
+        [TestMethod]
+        public void Add_Authorization_BearerWithSpaceAndNoValue()
+        {
+            var headers = new WebHeaderCollection();
+            headers.Add("Authorization: Bearer ");
+        }
+
+        [TestMethod]
+        public void Add_Authorization_NoSpaceSingleChar()
+        {
+            var headers = new WebHeaderCollection();
+            headers.Add("Authorization: 1");
+        }
+
+        [TestMethod]
+        public void Add_Authorization_ValidBearer()
+        {
+            var headers = new WebHeaderCollection();
+            headers.Add("Authorization: Bearer a11111");
+            string value = headers["Authorization"];
+            Assert.AreEqual("Bearer a11111", value);
+        }
+
+        [TestMethod]
+        public void Add_Authorization_ValidTestValue()
+        {
+            var headers = new WebHeaderCollection();
+            headers.Add("Authorization: test 1");
+            string value = headers["Authorization"];
+            Assert.AreEqual("test 1", value);
+        }
+
+        [TestMethod]
+        public void Add_Authorization_ValidSingleLetterPair()
+        {
+            var headers = new WebHeaderCollection();
+            headers.Add("Authorization: a b");
+            string value = headers["Authorization"];
+            Assert.AreEqual("a b", value);
+        }
+        [TestMethod]
+        public void Add_Authorization_EmptyValue()
+        {
+            var headers = new WebHeaderCollection();
+            headers.Add("Authorization:");
+            string value = headers["Authorization"];
+            Assert.AreEqual(string.Empty, value);
+        }
+
+        [TestMethod]
+        public void Add_Authorization_ColonWithSpaceOnly()
+        {
+            var headers = new WebHeaderCollection();
+            headers.Add("Authorization: ");
+            string value = headers["Authorization"];
+            Assert.AreEqual(string.Empty, value);
+        }
+
+        [TestMethod]
+        public void Add_NullHeader_ThrowsArgumentNullException()
+        {
+            var headers = new WebHeaderCollection();
+            Assert.ThrowsException(typeof(ArgumentNullException), () => headers.Add(null));
+        }
+
+        [TestMethod]
+        public void Add_EmptyHeader_ThrowsArgumentNullException()
+        {
+            var headers = new WebHeaderCollection();
+            Assert.ThrowsException(typeof(ArgumentNullException), () => headers.Add(string.Empty));
+        }
+
+        [TestMethod]
+        public void Add_HeaderWithNoColon_ThrowsArgumentException()
+        {
+            var headers = new WebHeaderCollection();
+            Assert.ThrowsException(typeof(ArgumentException), () => headers.Add("Authorization"));
+        }
+
+        [TestMethod]
+        public void Add_HeaderNameWithSpace_ThrowsArgumentException()
+        {
+            var headers = new WebHeaderCollection();
+            Assert.ThrowsException(typeof(ArgumentException), () => headers.Add("My Header: value"));
+        }
+    }
+}
diff --git a/nanoFramework.System.Net.Http/Http/System.Net.WebHeaders.cs b/nanoFramework.System.Net.Http/Http/System.Net.WebHeaders.cs
index 3aba84d..9587186 100644
--- a/nanoFramework.System.Net.Http/Http/System.Net.WebHeaders.cs
+++ b/nanoFramework.System.Net.Http/Http/System.Net.WebHeaders.cs
@@ -427,7 +427,16 @@ public void Add(string header)
             }
 
             string name = header.Substring(0, colpos);
-            string value = header.Substring(colpos + 1);
+            // Handle empty header value
+            string value;
+            if (colpos + 1 >= header.Length)
+            {
+                value = string.Empty;
+            }
+            else
+            {
+                value = header.Substring(colpos + 1);
+            }
 
             name = CheckBadChars(name, false);
             ThrowOnRestrictedHeader(name);