Index: src/runtime/lookup-asm/lookup-asm-x86_64-win64.S
==================================================================
--- src/runtime/lookup-asm/lookup-asm-x86_64-win64.S
+++ src/runtime/lookup-asm/lookup-asm-x86_64-win64.S
@@ -25,13 +25,16 @@
 .globl objc_msg_lookup_super_stret
 
 .section .text
 .macro generate_lookup name not_found
 \name:
-	test	%rcx, %rcx
+	test	rcx, rcx
 	jz	short ret_nil
 
+	bt	ecx, 0
+	jc	short .Ltagged_pointer_\name
+
 	mov	r8, [rcx]
 	mov	r8, [r8+56]
 
 .Lmain_\name:
 	mov	r10, rcx
@@ -55,10 +58,20 @@
 
 0:
 	mov	rcx, r10
 	mov	rdx, r11
 	jmp	\not_found
+
+.Ltagged_pointer_\name:
+	movzx	r8, cl
+	shr	r8, 1
+
+	mov	rax, offset objc_tagged_pointer_classes
+	mov	r8, [rax+r8*8]
+	mov	r8, [r8+56]
+
+	jmp	short .Lmain_\name
 .endm
 
 .macro generate_lookup_super name lookup
 \name:
 	mov	r8, rcx