diff --git a/Harmony/Internal/MethodCopier.cs b/Harmony/Internal/MethodCopier.cs
index 6a7dcac6..1a7b7590 100644
--- a/Harmony/Internal/MethodCopier.cs
+++ b/Harmony/Internal/MethodCopier.cs
@@ -214,8 +214,8 @@ void ParseExceptions()
 				var instr2 = GetInstruction(handler_end, true);
 				instr2.blocks.Add(new ExceptionBlock(ExceptionBlockType.EndExceptionBlock, null));
 
-				// The FilterOffset property is meaningful only for Filter clauses. 
-				// The CatchType property is not meaningful for Filter or Finally clauses. 
+				// The FilterOffset property is meaningful only for Filter clauses.
+				// The CatchType property is not meaningful for Filter or Finally clauses.
 				//
 				switch (exception.Flags)
 				{
@@ -640,16 +640,20 @@ void ReadOperand(ILInstruction instruction)
 
 		ILInstruction GetInstruction(int offset, bool isEndOfInstruction)
 		{
+			if (offset < 0)
+				throw new ArgumentOutOfRangeException(nameof(offset), offset, $"Instruction offset {offset} is less than 0");
+
 			var lastInstructionIndex = ilInstructions.Count - 1;
-			if (offset < 0 || offset > ilInstructions[lastInstructionIndex].offset)
-				throw new Exception($"Instruction offset {offset} is outside valid range 0 - {ilInstructions[lastInstructionIndex].offset}");
+			var instruction = ilInstructions[lastInstructionIndex];
+			if (offset > instruction.offset + instruction.GetSize() - 1)
+				throw new ArgumentOutOfRangeException(nameof(offset), offset, $"Instruction offset {offset} is outside valid range 0 - {instruction.offset + instruction.GetSize() - 1}");
 
 			var min = 0;
 			var max = lastInstructionIndex;
 			while (min <= max)
 			{
 				var mid = min + ((max - min) / 2);
-				var instruction = ilInstructions[mid];
+				instruction = ilInstructions[mid];
 
 				if (isEndOfInstruction)
 				{
diff --git a/HarmonyTests/HarmonyTests.csproj b/HarmonyTests/HarmonyTests.csproj
index 80cd81b0..950e7312 100644
--- a/HarmonyTests/HarmonyTests.csproj
+++ b/HarmonyTests/HarmonyTests.csproj
@@ -62,6 +62,10 @@
 		<PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.2" PrivateAssets="all" />
 	</ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">
+    <Reference Include="System.Web" />
+  </ItemGroup>
+
 	<ItemGroup>
 		<PackageReference Include="MonoMod.Common" Version="$(MonoModCommonVersion)" />
 	</ItemGroup>
diff --git a/HarmonyTests/IL/TestMethodBodyReader.cs b/HarmonyTests/IL/TestMethodBodyReader.cs
index 8f46615a..f983195a 100644
--- a/HarmonyTests/IL/TestMethodBodyReader.cs
+++ b/HarmonyTests/IL/TestMethodBodyReader.cs
@@ -1,15 +1,30 @@
 using HarmonyLib;
 using HarmonyLibTests.Assets;
 using NUnit.Framework;
+using System;
 using System.Collections;
 using System.Reflection;
 using System.Reflection.Emit;
+using System.Web;
 
 namespace HarmonyLibTests.IL
 {
 	[TestFixture]
 	public class TestMethodBodyReader : TestLogger
 	{
+#if NETFRAMEWORK
+		[Test]
+		public void FixIssue449()
+		{
+			var method = typeof(HttpRuntime).GetMethod("ReleaseResourcesAndUnloadAppDomain", BindingFlags.Instance | BindingFlags.NonPublic);
+
+			if (Environment.OSVersion.Platform != PlatformID.Win32NT) return;
+
+			Assert.NotNull(method);
+
+			Assert.AreEqual(29, MethodBodyReader.GetInstructions(null, method).Count);
+		}
+#endif
 		[Test]
 		public void Test_CanGetInstructionsWithNoILGenerator()
 		{