diff --git a/kernel/user-timer.cpp b/kernel/user-timer.cpp
index e0a653b2..1fb0f7ed 100644
--- a/kernel/user-timer.cpp
+++ b/kernel/user-timer.cpp
@@ -19,6 +19,7 @@
 
 #include <sys/types.h>
 
+#include <assert.h>
 #include <errno.h>
 #include <limits.h>
 #include <timespec.h>
@@ -261,25 +262,43 @@ int sys_clock_nanosleep(clockid_t clockid,
                         const struct timespec* user_duration,
                         struct timespec* user_remainder)
 {
+	assert(Interrupt::IsEnabled());
+
 	struct timespec time;
 
+	assert(Interrupt::IsEnabled());
 	Clock* clock = Time::GetClock(clockid);
+	assert(Interrupt::IsEnabled());
 	if ( !clock )
+	{
+		assert(Interrupt::IsEnabled());
 		return -1;
+	}
 
 	if ( !CopyFromUser(&time, user_duration, sizeof(time)) )
+	{
+		assert(Interrupt::IsEnabled());
 		return -1;
+	}
 
 	if ( !timespec_is_canonical(time) )
 		return errno = EINVAL, -1;
 
+	assert(Interrupt::IsEnabled());
 	time = flags & TIMER_ABSTIME ? clock->SleepUntil(time) :
 	                               clock->SleepDelay(time);
+	assert(Interrupt::IsEnabled());
 
 	if ( user_remainder && !CopyToUser(user_remainder, &time, sizeof(time)) )
+	{
+		assert(Interrupt::IsEnabled());
 		return -1;
+	}
 
-	return timespec_eq(time, timespec_nul()) ? 0 : (errno = EINTR, -1);
+	assert(Interrupt::IsEnabled());
+	int result = timespec_eq(time, timespec_nul()) ? 0 : (errno = EINTR, -1);
+	assert(Interrupt::IsEnabled());
+	return result;
 }
 
 int sys_timens(struct tmns* user_tmns)
diff --git a/kernel/x64/syscall.S b/kernel/x64/syscall.S
index c5f065c9..2eb5ab05 100644
--- a/kernel/x64/syscall.S
+++ b/kernel/x64/syscall.S
@@ -30,7 +30,17 @@ syscall_handler:
 	pushq %rbp
 	movq %rsp, %rbp
 
+	pushq %rax
+	sub $8, %rsp
+
+	pushf
+	pop %r10
+	mov $0x200, %r11
+	test %r10, %r11
+	jz 5f
+
 	# Make sure the requested system call is valid, if not, then fix it.
+	mov %rax, %r10
 	cmp $SYSCALL_MAX_NUM, %rax
 	jae 3f
 
@@ -44,6 +54,13 @@ syscall_handler:
 	# Call the system call.
 	callq *%rax
 
+	pushf
+	pop %rsi
+	mov $0x200, %r8
+	test %rsi, %r8
+	jz 6f
+	addq $16, %rsp
+
 	# Return to user-space, system call result in %rax:%rdx, errno in %ecx.
 	popq %rbp
 	movl errno, %ecx
@@ -91,4 +108,25 @@ syscall_handler:
 	xor %r8, %r8
 	jmp 2b
 
+5:
+	mov $syscall_interrupt_string_before, %rdi
+	jmp 7f
+6:
+	mov $syscall_interrupt_string_after, %rdi
+	jmp 7f
+7:
+	add $8, %rsp
+	pop %rsi
+	call PanicF
+
 .size syscall_handler, .-syscall_handler
+
+	.section	.rodata
+	.type	syscall_interrupt_string_before, @object
+	.size	syscall_interrupt_string_before, 56
+syscall_interrupt_string_before:
+	.string	"System call %u exited without interrupts enabled before"
+	.type	syscall_interrupt_string_after, @object
+	.size	syscall_interrupt_string_after, 55
+syscall_interrupt_string_after:
+	.string	"System call %u exited without interrupts enabled after"