diff --git a/sys/amd64/include/reg.h b/sys/amd64/include/reg.h
index 9ca092fea104..89211a32651b 100644
--- a/sys/amd64/include/reg.h
+++ b/sys/amd64/include/reg.h
@@ -56,8 +56,12 @@ struct reg {
 	register_t	r_rdx;
 	register_t	r_rcx;
 	register_t	r_rax;
-	register_t	r_trapno;
-	register_t	r_err;
+	uint32_t	r_trapno;
+	uint16_t	r_fs;
+	uint16_t	r_gs;
+	uint32_t	r_err;
+	uint16_t	r_es;
+	uint16_t	r_ds;
 	register_t	r_rip;
 	register_t	r_cs;
 	register_t	r_rflags;
diff --git a/sys/amd64/include/ucontext.h b/sys/amd64/include/ucontext.h
index 5c1380336321..c5bbd65b5a30 100644
--- a/sys/amd64/include/ucontext.h
+++ b/sys/amd64/include/ucontext.h
@@ -32,9 +32,16 @@
 #ifndef _MACHINE_UCONTEXT_H_
 #define	_MACHINE_UCONTEXT_H_
 
+/*
+ * mc_trapno bits. Shall be in sync with TF_XXX.
+ */
+#define	_MC_HASSEGS	0x1
+#define	_MC_HASBASES	0x2
+#define	_MC_FLAG_MASK	(_MC_HASSEGS | _MC_HASBASES)
+
 typedef struct __mcontext {
 	/*
-	 * The first 20 fields must match the definition of
+	 * The first 24 fields must match the definition of
 	 * sigcontext. So that we can support sigcontext
 	 * and ucontext_t at the same time.
 	 */
@@ -54,9 +61,13 @@ typedef struct __mcontext {
 	__register_t	mc_r13;
 	__register_t	mc_r14;
 	__register_t	mc_r15;
-	__register_t	mc_trapno;
+	__uint32_t	mc_trapno;
+	__uint16_t	mc_fs;
+	__uint16_t	mc_gs;
 	__register_t	mc_addr;
-	__register_t	mc_flags;
+	__uint32_t	mc_flags;
+	__uint16_t	mc_es;
+	__uint16_t	mc_ds;
 	__register_t	mc_err;
 	__register_t	mc_rip;
 	__register_t	mc_cs;
@@ -65,6 +76,7 @@ typedef struct __mcontext {
 	__register_t	mc_ss;
 
 	long	mc_len;			/* sizeof(mcontext_t) */
+
 #define	_MC_FPFMT_NODEV		0x10000	/* device not present or configured */
 #define	_MC_FPFMT_XMM		0x10002
 	long	mc_fpformat;
@@ -76,7 +88,11 @@ typedef struct __mcontext {
 	 * See <machine/fpu.h> for the internals of mc_fpstate[].
 	 */
 	long	mc_fpstate[64] __aligned(16);
-	long	mc_spare[8];
+
+	__register_t	mc_fsbase;
+	__register_t	mc_gsbase;
+
+	long	mc_spare[6];
 } mcontext_t;
 
 #endif /* !_MACHINE_UCONTEXT_H_ */
diff --git a/sys/compat/ia32/ia32_signal.h b/sys/compat/ia32/ia32_signal.h
index f2be96d5100b..6ebb0defc634 100644
--- a/sys/compat/ia32/ia32_signal.h
+++ b/sys/compat/ia32/ia32_signal.h
@@ -59,7 +59,9 @@ struct ia32_mcontext {
 	 * See <i386/include/npx.h> for the internals of mc_fpstate[].
 	 */
 	u_int32_t	mc_fpstate[128] __aligned(16);
-	u_int32_t	mc_spare2[8];
+	u_int32_t	mc_fsbase;
+	u_int32_t	mc_gsbase;
+	u_int32_t	mc_spare2[6];
 };
 
 struct ia32_ucontext {
diff --git a/sys/i386/include/ucontext.h b/sys/i386/include/ucontext.h
index c992495fedf8..d8657d3e6f6d 100644
--- a/sys/i386/include/ucontext.h
+++ b/sys/i386/include/ucontext.h
@@ -72,10 +72,15 @@ typedef struct __mcontext {
 	 * See <machine/npx.h> for the internals of mc_fpstate[].
 	 */
 	int	mc_fpstate[128] __aligned(16);
-	int	mc_spare2[8];
+
+	__register_t mc_fsbase;
+	__register_t mc_gsbase;
+
+	int	mc_spare2[6];
 } mcontext_t;
 
 #if defined(_KERNEL) && defined(COMPAT_FREEBSD4)
+
 struct mcontext4 {
 	__register_t	mc_onstack;	/* XXX - sigcontext compat. */
 	__register_t	mc_gs;		/* machine state (struct trapframe) */