diff --git a/src/system/kernel/arch/x86/arch_interrupts.S b/src/system/kernel/arch/x86/arch_interrupts.S
index 344ac03e9f..96a98505d0 100644
--- a/src/system/kernel/arch/x86/arch_interrupts.S
+++ b/src/system/kernel/arch/x86/arch_interrupts.S
@@ -378,7 +378,7 @@ trap99:
   1:
     movl	THREAD_flags(%edi), %eax
 	movl	%eax, %edx
-    orl		$THREAD_FLAGS_64_BIT_SYSCALL_RETURN, %edx
+    andl	$~THREAD_FLAGS_64_BIT_SYSCALL_RETURN, %edx
     lock
     cmpxchgl	%edx, THREAD_flags(%edi)
     jnz		1b