Index: src/runtime/lookup-asm/lookup-asm-x86-elf.S
==================================================================
--- src/runtime/lookup-asm/lookup-asm-x86-elf.S
+++ src/runtime/lookup-asm/lookup-asm-x86-elf.S
@@ -61,12 +61,13 @@
 	add	eax, offset _GLOBAL_OFFSET_TABLE_
 	lea	eax, [eax+\not_found@GOTOFF]
 	jmp	eax
 
 .Ltagged_pointer_\name:
+	and	dl, 0xF
+	shr	dl, 1
 	movzx	edx, dl
-	shr	edx, 1
 
 	call	get_eip
 	add	eax, offset _GLOBAL_OFFSET_TABLE_
 
 	lea	eax, [eax+objc_tagged_pointer_classes@GOTOFF]

Index: src/runtime/lookup-asm/lookup-asm-x86-win32.S
==================================================================
--- src/runtime/lookup-asm/lookup-asm-x86-win32.S
+++ src/runtime/lookup-asm/lookup-asm-x86-win32.S
@@ -53,12 +53,13 @@
 	jz	\not_found
 
 	ret
 
 .Ltagged_pointer_\name:
+	and	dl, 0xF
+	shr	dl, 1
 	movzx	edx, dl
-	shr	edx, 1
 
 	mov	eax, offset _objc_tagged_pointer_classes
 	mov	edx, [eax+edx*4]
 	mov	edx, [edx+32]
 

Index: src/runtime/lookup-asm/lookup-asm-x86_64-elf.S
==================================================================
--- src/runtime/lookup-asm/lookup-asm-x86_64-elf.S
+++ src/runtime/lookup-asm/lookup-asm-x86_64-elf.S
@@ -54,12 +54,13 @@
 	jz	short \not_found@PLT
 
 	ret
 
 .Ltagged_pointer_\name:
+	and	dil, 0xF
+	shr	dil, 1
 	movzx	r8, dil
-	shr	r8, 1
 
 	mov	rax, [rip+objc_tagged_pointer_classes@GOTPCREL]
 	mov	r8, [rax+r8*8]
 	mov	r8, [r8+64]
 

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
@@ -60,12 +60,13 @@
 	mov	rcx, r10
 	mov	rdx, r11
 	jmp	\not_found
 
 .Ltagged_pointer_\name:
+	and	cl, 0xF
+	shr	cl, 1
 	movzx	r8, cl
-	shr	r8, 1
 
 	mov	rax, offset objc_tagged_pointer_classes
 	mov	r8, [rax+r8*8]
 	mov	r8, [r8+56]
 

Index: src/runtime/tagged-pointer.m
==================================================================
--- src/runtime/tagged-pointer.m
+++ src/runtime/tagged-pointer.m
@@ -17,11 +17,12 @@
 
 #import "ObjFWRT.h"
 
 #import "private.h"
 
-#define NUM_TAGGED_POINTER_CLASSES 0x7F
+#define TAGGED_POINTER_BITS 4
+#define NUM_TAGGED_POINTER_CLASSES (1 << (TAGGED_POINTER_BITS - 1))
 
 Class objc_tagged_pointer_classes[NUM_TAGGED_POINTER_CLASSES];
 static uint_fast8_t taggedPointerClassesCount;
 
 int_fast8_t
@@ -47,11 +48,11 @@
 Class
 object_getTaggedPointerClass(id object)
 {
 	uintptr_t pointer = (uintptr_t)object;
 
-	pointer &= 0x7E;
+	pointer &= (1 << TAGGED_POINTER_BITS) - 1;
 	pointer >>= 1;
 
 	if (pointer >= NUM_TAGGED_POINTER_CLASSES)
 		return Nil;
 
@@ -61,12 +62,11 @@
 uintptr_t
 object_getTaggedPointerValue(id object)
 {
 	uintptr_t pointer = (uintptr_t)object;
 
-	pointer &= ~(uintptr_t)0xFF;
-	pointer >>= 8;
+	pointer >>= TAGGED_POINTER_BITS;
 
 	return pointer;
 }
 
 id
@@ -75,13 +75,13 @@
 	uintptr_t pointer;
 
 	if (class >= NUM_TAGGED_POINTER_CLASSES)
 		return nil;
 
-	if (value > (UINTPTR_MAX >> 8))
+	if (value > (UINTPTR_MAX >> TAGGED_POINTER_BITS))
 		return nil;
 
 	pointer = (class << 1) | 1;
-	pointer |= (value << 8);
+	pointer |= (value << TAGGED_POINTER_BITS);
 
 	return (id)pointer;
 }