diff --git a/WhiteMagicTest/StubAssemblerTests.cs b/WhiteMagicTest/StubAssemblerTests.cs
index 53dfa9c..0244328 100644
--- a/WhiteMagicTest/StubAssemblerTests.cs
+++ b/WhiteMagicTest/StubAssemblerTests.cs
@@ -2,11 +2,6 @@ using WhiteMagic.Assembly;
 
 namespace WhiteMagicTest;
 
-/// <summary>
-/// Tests for <see cref="StubAssembler"/> emit primitives (<see cref="StubAssembler.EmitU8"/>,
-/// <see cref="StubAssembler.EmitU32"/>, <see cref="StubAssembler.EmitU64"/>) and
-/// calling-convention stub encoding.
-/// </summary>
 public class StubAssemblerTests
 {
     private static StubAssembler Create() => new();
@@ -76,67 +71,171 @@ public class StubAssemblerTests
         Assert.Throws<NotSupportedException>(() => sut.Assemble("nop", 0));
     }
 
-    // ── Calling convention: x86 cdecl ──────────────────────────────────────
+    // ── x86 cdecl ──────────────────────────────────────────────────────────
 
     [Fact]
-    public void Cdecl_stub_with_zero_args_is_call_then_ret()
+    public void Cdecl_stub_zero_args_call_then_ret()
     {
         var sut = Create();
-        IntPtr stubAddr = (IntPtr)0x10000000;
-        IntPtr target = (IntPtr)0x12345678;
-        uint[] args = [];
+        uint rel32 = 0x12345678u - (0x10000000u + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [], 4, CallingConvention.Cdecl);
 
-        uint rel32 = (uint)target - ((uint)stubAddr + 5);
-        byte[] stub = sut.BuildCallStub(stubAddr, target, args, 4, CallingConvention.Cdecl);
-
-        Assert.Equal(6, stub.Length);
-        Assert.Equal(0xE8, stub[0]);                           // call
-        Assert.Equal(rel32, BitConverter.ToUInt32(stub, 1));   // rel32
-        Assert.Equal(0xC3, stub[5]);                           // ret
+        Assert.Equal([0xE8, (byte)rel32, (byte)(rel32>>8), (byte)(rel32>>16), (byte)(rel32>>24), 0xC3], stub);
     }
 
     [Fact]
-    public void Cdecl_stub_one_arg_reverse_push_then_call_then_cleanup()
+    public void Cdecl_stub_one_arg_push_call_cleanup_ret()
     {
         var sut = Create();
-        IntPtr stubAddr = (IntPtr)0x10000000;
-        IntPtr target = (IntPtr)0x12345678;
-        uint[] args = [0xAABBCCDD];
+        uint callAddr = 0x10000000u + 5;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0xAABBCCDD], 4, CallingConvention.Cdecl);
 
-        uint callAddr = (uint)stubAddr + 5;
-        uint rel32 = (uint)target - (callAddr + 5);
-        byte[] stub = sut.BuildCallStub(stubAddr, target, args, 4, CallingConvention.Cdecl);
-
-        byte[] expected = [
-            0x68, 0xDD, 0xCC, 0xBB, 0xAA, // push 0xAABBCCDD
-            0xE8,
-            (byte)rel32, (byte)(rel32 >> 8), (byte)(rel32 >> 16), (byte)(rel32 >> 24),
-            0x83, 0xC4, 0x04,              // add esp, 4
-            0xC3                            // ret
-        ];
-        Assert.Equal(expected, stub);
+        Assert.Equal([
+            0x68, 0xDD, 0xCC, 0xBB, 0xAA,
+            0xE8, (byte)rel32, (byte)(rel32>>8), (byte)(rel32>>16), (byte)(rel32>>24),
+            0x83, 0xC4, 0x04,
+            0xC3
+        ], stub);
     }
 
     [Fact]
     public void Cdecl_stub_two_args_reverse_order()
     {
         var sut = Create();
-        IntPtr stubAddr = (IntPtr)0x10000000;
-        IntPtr target = (IntPtr)0x12345678;
-        uint[] args = [0x11111111, 0x22222222];
+        uint callAddr = 0x10000000u + 10;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0x11111111, 0x22222222], 4, CallingConvention.Cdecl);
 
-        uint callAddr = (uint)stubAddr + 10;
-        uint rel32 = (uint)target - (callAddr + 5);
-        byte[] stub = sut.BuildCallStub(stubAddr, target, args, 4, CallingConvention.Cdecl);
-
-        byte[] expected = [
-            0x68, 0x22, 0x22, 0x22, 0x22, // push arg1 (reverse order)
-            0x68, 0x11, 0x11, 0x11, 0x11, // push arg0
-            0xE8,
-            (byte)rel32, (byte)(rel32 >> 8), (byte)(rel32 >> 16), (byte)(rel32 >> 24),
-            0x83, 0xC4, 0x08,              // add esp, 8
+        Assert.Equal([
+            0x68, 0x22, 0x22, 0x22, 0x22,
+            0x68, 0x11, 0x11, 0x11, 0x11,
+            0xE8, (byte)rel32, (byte)(rel32>>8), (byte)(rel32>>16), (byte)(rel32>>24),
+            0x83, 0xC4, 0x08,
             0xC3
-        ];
-        Assert.Equal(expected, stub);
+        ], stub);
+    }
+
+    // ── x86 stdcall ────────────────────────────────────────────────────────
+
+    [Fact]
+    public void Stdcall_stub_one_arg_no_cleanup()
+    {
+        var sut = Create();
+        uint callAddr = 0x10000000u + 5;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0xAABBCCDD], 4, CallingConvention.Stdcall);
+
+        Assert.Equal([
+            0x68, 0xDD, 0xCC, 0xBB, 0xAA,
+            0xE8, (byte)rel32, (byte)(rel32>>8), (byte)(rel32>>16), (byte)(rel32>>24),
+            0xC3
+        ], stub);
+    }
+
+    [Fact]
+    public void Stdcall_stub_two_args_reverse_no_cleanup()
+    {
+        var sut = Create();
+        uint callAddr = 0x10000000u + 10;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0x11111111, 0x22222222], 4, CallingConvention.Stdcall);
+
+        Assert.Equal([
+            0x68, 0x22, 0x22, 0x22, 0x22,
+            0x68, 0x11, 0x11, 0x11, 0x11,
+            0xE8, (byte)rel32, (byte)(rel32>>8), (byte)(rel32>>16), (byte)(rel32>>24),
+            0xC3
+        ], stub);
+    }
+
+    // ── x86 thiscall ───────────────────────────────────────────────────────
+
+    [Fact]
+    public void Thiscall_stub_ecx_then_stack_then_call()
+    {
+        var sut = Create();
+        uint callAddr = 0x10000000u + 10;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0xAAAA5555, 0xBBBB6666], 4, CallingConvention.Thiscall);
+
+        Assert.Equal([
+            0xB9, 0x55, 0x55, 0xAA, 0xAA,
+            0x68, 0x66, 0x66, 0xBB, 0xBB,
+            0xE8, (byte)rel32, (byte)(rel32>>8), (byte)(rel32>>16), (byte)(rel32>>24),
+            0xC3
+        ], stub);
+    }
+
+    [Fact]
+    public void Thiscall_stub_one_arg_ecx_only_then_call()
+    {
+        var sut = Create();
+        uint callAddr = 0x10000000u + 5;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0xCAFEBABE], 4, CallingConvention.Thiscall);
+
+        Assert.Equal(11, stub.Length);
+        Assert.Equal(0xB9, stub[0]);
+        Assert.Equal(0xCAFEBABE, BitConverter.ToUInt32(stub, 1));
+        Assert.Equal(0xE8, stub[5]);
+        Assert.Equal(rel32, BitConverter.ToUInt32(stub, 6));
+        Assert.Equal(0xC3, stub[10]);
+    }
+
+    // ── x86 fastcall ───────────────────────────────────────────────────────
+
+    [Fact]
+    public void Fastcall_stub_ecx_edx_stack_call()
+    {
+        var sut = Create();
+        uint callAddr = 0x10000000u + 15;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0x11111111, 0x22222222, 0x33333333], 4, CallingConvention.Fastcall);
+
+        Assert.Equal([
+            0xB9, 0x11, 0x11, 0x11, 0x11,
+            0xBA, 0x22, 0x22, 0x22, 0x22,
+            0x68, 0x33, 0x33, 0x33, 0x33,
+            0xE8, (byte)rel32, (byte)(rel32>>8), (byte)(rel32>>16), (byte)(rel32>>24),
+            0xC3
+        ], stub);
+    }
+
+    [Fact]
+    public void Fastcall_stub_two_args_registers_only()
+    {
+        var sut = Create();
+        uint callAddr = 0x10000000u + 10;
+        uint rel32 = 0x12345678u - (callAddr + 5);
+        byte[] stub = sut.BuildCallStub(
+            (IntPtr)0x10000000, (IntPtr)0x12345678, [0xAAAAAAAA, 0xBBBBBBBB], 4, CallingConvention.Fastcall);
+
+        Assert.Equal(16, stub.Length);
+        Assert.Equal(0xB9, stub[0]);
+        Assert.Equal(0xAAAAAAAA, BitConverter.ToUInt32(stub, 1));
+        Assert.Equal(0xBA, stub[5]);
+        Assert.Equal(0xBBBBBBBB, BitConverter.ToUInt32(stub, 6));
+        Assert.Equal(0xE8, stub[10]);
+        Assert.Equal(rel32, BitConverter.ToUInt32(stub, 11));
+        Assert.Equal(0xC3, stub[15]);
+    }
+
+    // ── x64 ────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public void X64_stub_throws_not_implemented_by_default()
+    {
+        var sut = Create();
+        Assert.Throws<NotImplementedException>(() =>
+            sut.BuildCallStub((IntPtr)0x10000000, (IntPtr)0x12345678, [], 8, CallingConvention.Cdecl));
     }
 }