diff --git a/src/Microsoft.AspNetCore.Server.Kestrel/Internal/Http/FrameHeaders.cs b/src/Microsoft.AspNetCore.Server.Kestrel/Internal/Http/FrameHeaders.cs
index c6b9d0c59..4d234322a 100644
--- a/src/Microsoft.AspNetCore.Server.Kestrel/Internal/Http/FrameHeaders.cs
+++ b/src/Microsoft.AspNetCore.Server.Kestrel/Internal/Http/FrameHeaders.cs
@@ -233,16 +233,41 @@ public static void ValidateHeaderCharacters(string headerCharacters)
             }
         }
 
-        public static long ParseContentLength(StringValues value)
+        public static unsafe long ParseContentLength(StringValues value)
         {
-            try
-            {
-                return long.Parse(value, NumberStyles.AllowLeadingWhite | NumberStyles.AllowTrailingWhite, CultureInfo.InvariantCulture);
-            }
-            catch (FormatException ex)
+            var input = value.ToString();
+            var parsed = 0L;
+
+            fixed (char* ptr = input)
             {
-                throw new InvalidOperationException("Content-Length value must be an integral number.", ex);
+                var ch = (ushort*)ptr;
+                var end = ch + input.Length;
+
+                if (ch == end)
+                {
+                    ThrowInvalidContentLengthException(value);
+                }
+
+                ushort digit = 0;
+                while (ch < end && (digit = (ushort)(*ch - 0x30)) <= 9)
+                {
+                    parsed *= 10;
+                    parsed += digit;
+                    ch++;
+                }
+
+                if (ch != end)
+                {
+                    ThrowInvalidContentLengthException(value);
+                }
             }
+
+            return parsed;
+        }
+
+        private static void ThrowInvalidContentLengthException(string value)
+        {
+            throw new InvalidOperationException($"Invalid Content-Length: \"{value}\". Value must be a positive integral number.");
         }
 
         private static void ThrowInvalidHeaderCharacter(char ch)
diff --git a/test/Microsoft.AspNetCore.Server.KestrelTests/FrameResponseHeadersTests.cs b/test/Microsoft.AspNetCore.Server.KestrelTests/FrameResponseHeadersTests.cs
index c21d6b242..bc76f2c09 100644
--- a/test/Microsoft.AspNetCore.Server.KestrelTests/FrameResponseHeadersTests.cs
+++ b/test/Microsoft.AspNetCore.Server.KestrelTests/FrameResponseHeadersTests.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Text;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Server.Kestrel;
@@ -149,75 +150,88 @@ public void ThrowsWhenClearingHeadersAfterReadOnlyIsSet()
             Assert.Throws<InvalidOperationException>(() => dictionary.Clear());
         }
 
-        [Fact]
-        public void ThrowsWhenAddingContentLengthWithNonNumericValue()
+        [Theory]
+        [MemberData(nameof(BadContentLengths))]
+        public void ThrowsWhenAddingContentLengthWithNonNumericValue(string contentLength)
         {
             var headers = new FrameResponseHeaders();
             var dictionary = (IDictionary<string, StringValues>)headers;
 
-            Assert.Throws<InvalidOperationException>(() => dictionary.Add("Content-Length", new[] { "bad" }));
+            var exception = Assert.Throws<InvalidOperationException>(() => dictionary.Add("Content-Length", new[] { contentLength }));
+            Assert.Equal($"Invalid Content-Length: \"{contentLength}\". Value must be a positive integral number.", exception.Message);
         }
 
-        [Fact]
-        public void ThrowsWhenSettingContentLengthToNonNumericValue()
+        [Theory]
+        [MemberData(nameof(BadContentLengths))]
+        public void ThrowsWhenSettingContentLengthToNonNumericValue(string contentLength)
         {
             var headers = new FrameResponseHeaders();
             var dictionary = (IDictionary<string, StringValues>)headers;
 
-            Assert.Throws<InvalidOperationException>(() => ((IHeaderDictionary)headers)["Content-Length"] = "bad");
+            var exception = Assert.Throws<InvalidOperationException>(() => ((IHeaderDictionary)headers)["Content-Length"] = contentLength);
+            Assert.Equal($"Invalid Content-Length: \"{contentLength}\". Value must be a positive integral number.", exception.Message);
         }
 
-        [Fact]
-        public void ThrowsWhenSettingRawContentLengthToNonNumericValue()
+        [Theory]
+        [MemberData(nameof(BadContentLengths))]
+        public void ThrowsWhenSettingRawContentLengthToNonNumericValue(string contentLength)
         {
             var headers = new FrameResponseHeaders();
 
-            Assert.Throws<InvalidOperationException>(() => headers.SetRawContentLength("bad", Encoding.ASCII.GetBytes("bad")));
+            var exception = Assert.Throws<InvalidOperationException>(() => headers.SetRawContentLength(contentLength, Encoding.ASCII.GetBytes(contentLength)));
+            Assert.Equal($"Invalid Content-Length: \"{contentLength}\". Value must be a positive integral number.", exception.Message);
         }
 
-        [Fact]
-        public void ThrowsWhenAssigningHeaderContentLengthToNonNumericValue()
+        [Theory]
+        [MemberData(nameof(BadContentLengths))]
+        public void ThrowsWhenAssigningHeaderContentLengthToNonNumericValue(string contentLength)
         {
             var headers = new FrameResponseHeaders();
-            Assert.Throws<InvalidOperationException>(() => headers.HeaderContentLength = "bad");
+
+            var exception = Assert.Throws<InvalidOperationException>(() => headers.HeaderContentLength = contentLength);
+            Assert.Equal($"Invalid Content-Length: \"{contentLength}\". Value must be a positive integral number.", exception.Message);
         }
 
-        [Fact]
-        public void ContentLengthValueCanBeReadAsLongAfterAddingHeader()
+        [Theory]
+        [MemberData(nameof(GoodContentLengths))]
+        public void ContentLengthValueCanBeReadAsLongAfterAddingHeader(string contentLength)
         {
             var headers = new FrameResponseHeaders();
             var dictionary = (IDictionary<string, StringValues>)headers;
-            dictionary.Add("Content-Length", "42");
+            dictionary.Add("Content-Length", contentLength);
 
-            Assert.Equal(42, headers.HeaderContentLengthValue);
+            Assert.Equal(ParseLong(contentLength), headers.HeaderContentLengthValue);
         }
 
-        [Fact]
-        public void ContentLengthValueCanBeReadAsLongAfterSettingHeader()
+        [Theory]
+        [MemberData(nameof(GoodContentLengths))]
+        public void ContentLengthValueCanBeReadAsLongAfterSettingHeader(string contentLength)
         {
             var headers = new FrameResponseHeaders();
             var dictionary = (IDictionary<string, StringValues>)headers;
-            dictionary["Content-Length"] = "42";
+            dictionary["Content-Length"] = contentLength;
 
-            Assert.Equal(42, headers.HeaderContentLengthValue);
+            Assert.Equal(ParseLong(contentLength), headers.HeaderContentLengthValue);
         }
 
-        [Fact]
-        public void ContentLengthValueCanBeReadAsLongAfterSettingRawHeader()
+        [Theory]
+        [MemberData(nameof(GoodContentLengths))]
+        public void ContentLengthValueCanBeReadAsLongAfterSettingRawHeader(string contentLength)
         {
             var headers = new FrameResponseHeaders();
-            headers.SetRawContentLength("42", Encoding.ASCII.GetBytes("42"));
+            headers.SetRawContentLength(contentLength, Encoding.ASCII.GetBytes(contentLength));
 
-            Assert.Equal(42, headers.HeaderContentLengthValue);
+            Assert.Equal(ParseLong(contentLength), headers.HeaderContentLengthValue);
         }
 
-        [Fact]
-        public void ContentLengthValueCanBeReadAsLongAfterAssigningHeader()
+        [Theory]
+        [MemberData(nameof(GoodContentLengths))]
+        public void ContentLengthValueCanBeReadAsLongAfterAssigningHeader(string contentLength)
         {
             var headers = new FrameResponseHeaders();
-            headers.HeaderContentLength = "42";
+            headers.HeaderContentLength = contentLength;
 
-            Assert.Equal(42, headers.HeaderContentLengthValue);
+            Assert.Equal(ParseLong(contentLength), headers.HeaderContentLengthValue);
         }
 
         [Fact]
@@ -243,5 +257,33 @@ public void ContentLengthValueClearedWhenHeadersCleared()
 
             Assert.Equal(null, headers.HeaderContentLengthValue);
         }
+
+        private static long ParseLong(string value)
+        {
+            return long.Parse(value, NumberStyles.AllowLeadingWhite | NumberStyles.AllowTrailingWhite, CultureInfo.InvariantCulture);
+        }
+
+        public static TheoryData<string> GoodContentLengths => new TheoryData<string>
+        {
+            "0",
+            "00",
+            "042",
+            "42",
+            long.MaxValue.ToString(CultureInfo.InvariantCulture)
+        };
+
+        public static TheoryData<string> BadContentLengths => new TheoryData<string>
+        {
+            "",
+            " ",
+            " 42",
+            "42 ",
+            "bad",
+            "!",
+            "!42",
+            "42!",
+            "42,000",
+            "42.000",
+        };
     }
-}
+}
\ No newline at end of file