diff --git a/arch/x86/kernel/include/ihk/context.h b/arch/x86/kernel/include/ihk/context.h
index 2aebc038..fe09451d 100644
--- a/arch/x86/kernel/include/ihk/context.h
+++ b/arch/x86/kernel/include/ihk/context.h
@@ -49,6 +49,7 @@ typedef struct x86_user_context ihk_mc_user_context_t;
 #define ihk_mc_syscall_arg5(uc) (uc)->gpr.r9
 
 #define ihk_mc_syscall_ret(uc)  (uc)->gpr.rax
+#define ihk_mc_syscall_number(uc)  (uc)->gpr.orig_rax
 
 #define ihk_mc_syscall_pc(uc)   (uc)->gpr.rip
 #define ihk_mc_syscall_sp(uc)   (uc)->gpr.rsp
diff --git a/arch/x86/kernel/include/registers.h b/arch/x86/kernel/include/registers.h
index 54912cbf..ba09b259 100644
--- a/arch/x86/kernel/include/registers.h
+++ b/arch/x86/kernel/include/registers.h
@@ -189,9 +189,30 @@ struct tss64 {
 } __attribute__((packed));
 
 struct x86_basic_regs {
-	unsigned long r15, r14, r13, r12, rbp, rbx, r11, r10;
-	unsigned long r9, r8, rax, rcx, rdx, rsi, rdi, error;
-	unsigned long rip, cs, rflags, rsp, ss;
+	unsigned long r15;
+	unsigned long r14;
+	unsigned long r13;
+	unsigned long r12;
+	unsigned long rbp;
+	unsigned long rbx;
+	unsigned long r11;
+	unsigned long r10;
+	unsigned long r9;
+	unsigned long r8;
+	unsigned long rax;
+	unsigned long rcx;
+	unsigned long rdx;
+	unsigned long rsi;
+	unsigned long rdi;
+	union {
+		unsigned long orig_rax; /* syscall */
+		unsigned long error;    /* interrupts */
+	};
+	unsigned long rip;
+	unsigned long cs;
+	unsigned long rflags;
+	unsigned long rsp;
+	unsigned long ss;
 };
 
 struct x86_sregs {
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 6ef6fc52..c6d9646f 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -9928,7 +9928,9 @@ long syscall(int num, ihk_mc_user_context_t *ctx)
 	cpu_enable_interrupt();
 
 	if (cpu_local_var(current)->proc->ptrace) {
+		ihk_mc_syscall_ret(ctx) = -ENOSYS;
 		ptrace_syscall_enter(cpu_local_var(current));
+		num = ihk_mc_syscall_number(ctx);
 	}
 
 #if 0