diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index b223b1b4d5cd..540c24f74837 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -93,6 +93,17 @@
 	hint	#20
 	.endm
 
+/*
+ * Sanitise a 64-bit bounded index wrt speculation, returning zero if out
+ * of bounds.
+ */
+	.macro	mask_nospec64, idx, limit, tmp
+	sub	\tmp, \idx, \limit
+	bic	\tmp, \tmp, \idx
+	and	\idx, \idx, \tmp, asr #63
+	csdb
+	.endm
+
 /*
  * NOP sequence
  */
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 3f1cd7a795bb..c154b1608405 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -795,6 +795,7 @@ el0_svc_naked:					// compat entry point
 	b.ne	__sys_trace
 	cmp     scno, sc_nr                     // check upper syscall limit
 	b.hs	ni_sys
+	mask_nospec64 scno, sc_nr, x19	// enforce bounds for syscall number
 	ldr	x16, [stbl, scno, lsl #3]	// address in the syscall table
 	blr	x16				// call sys_* routine
 	b	ret_fast_syscall