diff --git a/src/Runner.Sdk/ActionPlugin.cs b/src/Runner.Sdk/ActionPlugin.cs
index 35ffa9ab4..441f8ec02 100644
--- a/src/Runner.Sdk/ActionPlugin.cs
+++ b/src/Runner.Sdk/ActionPlugin.cs
@@ -73,7 +73,7 @@ namespace GitHub.Runner.Sdk
         {
             var headerValues = new List<ProductInfoHeaderValue>();
             headerValues.Add(new ProductInfoHeaderValue($"GitHubActionsRunner-Plugin", BuildConstants.RunnerPackage.Version));
-            headerValues.Add(new ProductInfoHeaderValue($"({RuntimeInformation.OSDescription.Trim()})"));
+            headerValues.Add(new ProductInfoHeaderValue($"({StringUtil.SanitizeUserAgentHeader(RuntimeInformation.OSDescription)})"));
 
             if (VssClientHttpRequestSettings.Default.UserAgent != null && VssClientHttpRequestSettings.Default.UserAgent.Count > 0)
             {
diff --git a/src/Runner.Sdk/Util/StringUtil.cs b/src/Runner.Sdk/Util/StringUtil.cs
index 3110e7e21..69cff219b 100644
--- a/src/Runner.Sdk/Util/StringUtil.cs
+++ b/src/Runner.Sdk/Util/StringUtil.cs
@@ -123,5 +123,12 @@ namespace GitHub.Runner.Sdk
         {
             return value?.Substring(0, Math.Min(value.Length, count));
         }
+
+        // Fixes format violations e.g. https://github.com/actions/runner/issues/2165
+        public static string SanitizeUserAgentHeader(string header)
+        {
+            return header.Replace("(", "[").Replace(")", "]").Trim();
+        }
+
     }
 }
diff --git a/src/Runner.Sdk/Util/VssUtil.cs b/src/Runner.Sdk/Util/VssUtil.cs
index 12cc5c118..b9b0f92d8 100644
--- a/src/Runner.Sdk/Util/VssUtil.cs
+++ b/src/Runner.Sdk/Util/VssUtil.cs
@@ -19,7 +19,7 @@ namespace GitHub.Runner.Sdk
         {
             var headerValues = new List<ProductInfoHeaderValue>();
             headerValues.AddRange(additionalUserAgents);
-            headerValues.Add(new ProductInfoHeaderValue($"({RuntimeInformation.OSDescription.Trim()})"));
+            headerValues.Add(new ProductInfoHeaderValue($"({StringUtil.SanitizeUserAgentHeader(RuntimeInformation.OSDescription)})"));
 
             if (VssClientHttpRequestSettings.Default.UserAgent != null && VssClientHttpRequestSettings.Default.UserAgent.Count > 0)
             {
diff --git a/src/Test/L0/Util/StringUtilL0.cs b/src/Test/L0/Util/StringUtilL0.cs
index e66181874..f6eed8ccf 100644
--- a/src/Test/L0/Util/StringUtilL0.cs
+++ b/src/Test/L0/Util/StringUtilL0.cs
@@ -1,5 +1,4 @@
-using GitHub.Runner.Common.Util;
-using GitHub.Runner.Sdk;
+using GitHub.Runner.Sdk;
 using System.Globalization;
 using Xunit;
 
@@ -186,5 +185,19 @@ namespace GitHub.Runner.Common.Tests.Util
                 Assert.False(result9, $"'{undefineString3}' should convert to false.");
             }
         }
+
+        [Theory]
+        [InlineData("", "")]
+        [InlineData("(())", "[[]]")]
+        [InlineData("()()", "[][]")]
+        [InlineData("  Liquorix kernel OS Description is poorly formatted (linux version ", "Liquorix kernel OS Description is poorly formatted [linux version")]
+        [InlineData("Liquorix kernel OS Description is poorly formatted (linux version", "Liquorix kernel OS Description is poorly formatted [linux version")]
+        [InlineData("()((.", "[][[.")]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Common")]
+        public void SanitizeUserAgentHeader(string input, string expected)
+        {
+            Assert.Equal(expected, StringUtil.SanitizeUserAgentHeader(input));
+        }
     }
 }