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
@@ -27,12 +27,12 @@
 \name:
 	movl	4(%esp), %edx
 	testl	%edx, %edx
 	jz	ret_nil
 
-	btl	$0, %edx
-	jc	.Ltagged_pointer_\name
+	testb	$1, %dl
+	jnz	.Ltagged_pointer_\name
 
 	movl	(%edx), %edx
 	movl	32(%edx), %edx
 
 .Lmain_\name:

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
@@ -25,12 +25,12 @@
 \name:
 	movl	4(%esp), %edx
 	testl	%edx, %edx
 	jz	ret_nil
 
-	btl	$0, %edx
-	jc	.Ltagged_pointer_\name
+	testb	$1, %dl
+	jnz	.Ltagged_pointer_\name
 
 	movl	(%edx), %edx
 	movl	32(%edx), %edx
 
 .Lmain_\name:

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
@@ -26,12 +26,12 @@
 .macro generate_lookup name not_found
 \name:
 	testq	%rdi, %rdi
 	jz	ret_nil
 
-	btl	$0, %edi
-	jc	.Ltagged_pointer_\name
+	testb	$1, %dil
+	jnz	.Ltagged_pointer_\name
 
 	movq	(%rdi), %r8
 	movq	64(%r8), %r8
 
 .Lmain_\name:

Index: src/runtime/lookup-asm/lookup-asm-x86_64-macho.S
==================================================================
--- src/runtime/lookup-asm/lookup-asm-x86_64-macho.S
+++ src/runtime/lookup-asm/lookup-asm-x86_64-macho.S
@@ -24,12 +24,12 @@
 .macro generate_lookup
 $0:
 	testq	%rdi, %rdi
 	jz	ret_nil
 
-	btl	$$0, %edi
-	jc	Ltagged_pointer_$0
+	testb	$$1, %dil
+	jnz	Ltagged_pointer_$0
 
 	movq	(%rdi), %r8
 	movq	64(%r8), %r8
 
 Lmain_$0:

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
@@ -26,12 +26,12 @@
 .macro generate_lookup name not_found
 \name:
 	test	rcx, rcx
 	jz	short ret_nil
 
-	bt	ecx, 0
-	jc	short .Ltagged_pointer_\name
+	test	cl, 1
+	jnz	short .Ltagged_pointer_\name
 
 	mov	r8, [rcx]
 	mov	r8, [r8+56]
 
 .Lmain_\name: