diff --git a/sys/arm/arm/exec_machdep.c b/sys/arm/arm/exec_machdep.c
--- a/sys/arm/arm/exec_machdep.c
+++ b/sys/arm/arm/exec_machdep.c
@@ -205,6 +205,8 @@
 		if (rv != 0)
 			return (rv);
 	}
+	mcp->mc_flags = _MC_TLS_VALID;
+	mcp->mc_tpidr = (register_t)get_tls();
 
 	return (0);
 }
@@ -272,6 +274,8 @@
 	if (vfp != NULL)
 		set_vfpcontext(td, vfp);
 #endif
+	if ((mcp->mc_flags & _MC_TLS_VALID) != 0)
+		set_tls((void *)mcp->mc_tpidr);
 	return (0);
 }
 
diff --git a/sys/arm/include/ucontext.h b/sys/arm/include/ucontext.h
--- a/sys/arm/include/ucontext.h
+++ b/sys/arm/include/ucontext.h
@@ -82,7 +82,10 @@
 	 */
 	__size_t	mc_vfp_size;
 	void 		*mc_vfp_ptr;
-	unsigned int	mc_spare[33];
+	unsigned int	mc_flags;
+#define _MC_TLS_VALID	0x2		/* Set when mc_tpidr is valid */
+        __greg_t	mc_tpidr;
+	unsigned int	mc_spare[31];
 } mcontext_t;
 
 #define UC_
diff --git a/sys/arm64/arm64/exec_machdep.c b/sys/arm64/arm64/exec_machdep.c
--- a/sys/arm64/arm64/exec_machdep.c
+++ b/sys/arm64/arm64/exec_machdep.c
@@ -455,6 +455,8 @@
 	mcp->mc_gpregs.gp_sp = tf->tf_sp;
 	mcp->mc_gpregs.gp_lr = tf->tf_lr;
 	mcp->mc_gpregs.gp_elr = tf->tf_elr;
+	mcp->mc_flags = _MC_TLS_VALID;
+	mcp->mc_tpidr = READ_SPECIALREG(tpidr_el0);
 	get_fpcontext(td, mcp);
 
 	return (0);
@@ -504,6 +506,8 @@
 		    READ_SPECIALREG(mdscr_el1) | MDSCR_SS);
 		isb();
 	}
+	if ((mcp->mc_flags & _MC_TLS_VALID) != 0)
+		WRITE_SPECIALREG(tpidr_el0, mcp->mc_tpidr);
 	set_fpcontext(td, mcp);
 
 	return (0);
diff --git a/sys/arm64/arm64/freebsd32_machdep.c b/sys/arm64/arm64/freebsd32_machdep.c
--- a/sys/arm64/arm64/freebsd32_machdep.c
+++ b/sys/arm64/arm64/freebsd32_machdep.c
@@ -195,6 +195,8 @@
 
 	mcp->mc_vfp_size = 0;
 	mcp->mc_vfp_ptr = 0;
+	mcp->mc_flags = _MC_TLS_VALID;
+	mcp->mc_tpidr = READ_SPECIALREG(tpidrro_el0);
 
 	memset(mcp->mc_spare, 0, sizeof(mcp->mc_spare));
 }
@@ -232,6 +234,11 @@
 		tf->tf_x[i] = mcp->mc_gregset[i];
 	tf->tf_elr = mcp->mc_gregset[15];
 	tf->tf_spsr = spsr;
+	if ((mcp->mc_flags & _MC_TLS_VALID) != 0) {
+		/* Set both to match cpu_set_user_tls */
+		WRITE_SPECIALREG(tpidr_el0, mcp->mc_tpidr);
+		WRITE_SPECIALREG(tpidrro_el0, mcp->mc_tpidr);
+	}
 #ifdef VFP
 	if (mcp->mc_vfp_size == sizeof(mc_vfp) && mcp->mc_vfp_ptr != 0) {
 		if (copyin((void *)(uintptr_t)mcp->mc_vfp_ptr, &mc_vfp,
diff --git a/sys/arm64/include/ucontext.h b/sys/arm64/include/ucontext.h
--- a/sys/arm64/include/ucontext.h
+++ b/sys/arm64/include/ucontext.h
@@ -54,8 +54,10 @@
 	struct fpregs	mc_fpregs;
 	int		mc_flags;
 #define	_MC_FP_VALID	0x1		/* Set when mc_fpregs has valid data */
+#define	_MC_TLS_VALID	0x2		/* Set when mc_tpidr is valid */
 	int		mc_pad;		/* Padding */
-	__uint64_t	mc_spare[8];	/* Space for expansion, set to zero */
+	__register_t	mc_tpidr;
+	__uint64_t	mc_spare[7];	/* Space for expansion, set to zero */
 };
 
 typedef struct __mcontext mcontext_t;
@@ -66,7 +68,9 @@
 	uint32_t		mc_gregset[17];
 	uint32_t		mc_vfp_size;
 	uint32_t		mc_vfp_ptr;
-	uint32_t		mc_spare[33];
+	uint32_t		mc_flags;
+	uint32_t		mc_tpidr;
+	uint32_t		mc_spare[31];
 } mcontext32_t;
 
 typedef struct __ucontext32 {