diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 7178865f48..854481f4f9 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -353,6 +353,7 @@ cpu_init_done:
 
         ldr   r0, =HSCTLR_SET
         mcr   CP32(r0, HSCTLR)
+        isb
 
         mov   pc, r5                        /* Return address is in r5 */
 ENDPROC(cpu_init)
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 057dd5d925..42a2177c53 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -485,6 +485,7 @@ cpu_init:
 
         ldr   x0, =SCTLR_EL2_SET
         msr   SCTLR_EL2, x0
+        isb
 
         /*
          * Ensure that any exceptions encountered at EL2