diff --git a/source/Indy.IL2CPU.IL.X86/Box.cs b/source/Indy.IL2CPU.IL.X86/Box.cs
index 55f1c2f46..d4aa02053 100644
--- a/source/Indy.IL2CPU.IL.X86/Box.cs
+++ b/source/Indy.IL2CPU.IL.X86/Box.cs
@@ -31,11 +31,15 @@ namespace Indy.IL2CPU.IL.X86 {
 		}
 
 		public override void DoAssemble() {
-			new CPUx86.Pushd("0x" + (ObjectImpl.FieldDataOffset + mTheSize + (4 - (mTheSize % 4))).ToString("X").ToUpper());
+			int xSize = mTheSize;
+			if (mTheSize % 4 != 0) {
+				xSize += 4 - (mTheSize % 4);
+			}
+			new CPUx86.Pushd("0x" + (ObjectImpl.FieldDataOffset + xSize).ToString("X").ToUpper());
 			new CPUx86.Call(CPU.Label.GenerateLabelName(RuntimeEngineRefs.Heap_AllocNewObjectRef));
 			new CPUx86.Move("dword", CPUx86.Registers.AtEAX, "0x" + mTypeId.ToString("X"));
 			new CPUx86.Move("dword", "[eax + 4]", "0x" + InstanceTypeEnum.BoxedValueType.ToString("X"));
-			for (int i = 0; i < ((mTheSize + (4 - (mTheSize % 4))) / 4); i++) {
+			for (int i = 0; i < (xSize / 4); i++) {
 				new CPUx86.Pop(CPUx86.Registers.EDX);
 				new CPUx86.Move("dword", "[eax + 0x" + (ObjectImpl.FieldDataOffset + (i * 4)).ToString("X") + "]", "edx");
 			}
diff --git a/source/Indy.IL2CPU.IL.X86/Isinst.cs b/source/Indy.IL2CPU.IL.X86/Isinst.cs
index a8c8cfc36..ecabcbb16 100644
--- a/source/Indy.IL2CPU.IL.X86/Isinst.cs
+++ b/source/Indy.IL2CPU.IL.X86/Isinst.cs
@@ -29,24 +29,24 @@ namespace Indy.IL2CPU.IL.X86 {
 
 		public override void DoAssemble() {
 			string mReturnNullLabel = mThisLabel + "_ReturnNull";
-			new CPUx86.Pop(CPUx86.Registers.EAX);
+			new CPUx86.Move(CPUx86.Registers.EAX, CPUx86.Registers.AtESP);
 			new CPUx86.Compare(CPUx86.Registers.EAX, "0");
 			new CPUx86.JumpIfZero(mReturnNullLabel);
-			new CPUx86.Pushd(CPUx86.Registers.AtEAX, "0" + mTypeId + "h");
+			new CPUx86.Pushd(CPUx86.Registers.AtEAX);
+			new CPUx86.Pushd("0" + mTypeId + "h");
+			Assembler.StackContents.Push(new StackContent(4, typeof(object)));
 			Assembler.StackContents.Push(new StackContent(4, typeof(object)));
 			MethodBase xMethodIsInstance = Engine.GetMethodBase(typeof(VTablesImpl), "IsInstance", "System.Int32", "System.Int32");
 			Engine.QueueMethod(xMethodIsInstance);
 			Op xOp = new Call(xMethodIsInstance, mCurrentILOffset);
 			xOp.Assembler = Assembler;
 			xOp.Assemble();
-			new CPUx86.Pop(CPUx86.Registers.EAX);
 			Assembler.StackContents.Pop();
+			new CPUx86.Pop(CPUx86.Registers.EAX);
 			new CPUx86.Compare(CPUx86.Registers.EAX, "0");
-			new CPUx86.JumpIfEquals(mReturnNullLabel);
-			new CPUx86.Pushd(CPUx86.Registers.EAX);
-			new CPUx86.JumpAlways(mNextOpLabel);
+			new CPUx86.JumpIfNotEquals(mNextOpLabel);
 			new CPU.Label(mReturnNullLabel);
-			Assembler.StackContents.Push(new StackContent(1, typeof(bool)));
+			new CPUx86.Add("esp", "4");
 			new CPUx86.Pushd("0");
 		}
 	}