diff --git a/embassy-rp/src/multicore.rs b/embassy-rp/src/multicore.rs
index 468e8470..89a2680a 100644
--- a/embassy-rp/src/multicore.rs
+++ b/embassy-rp/src/multicore.rs
@@ -74,7 +74,7 @@ fn install_stack_guard(stack_bottom: *mut usize) {
     let subregion_select = 0xff ^ (1 << ((addr >> 5) & 7));
     unsafe {
         core.MPU.ctrl.write(5); // enable mpu with background default map
-        core.MPU.rbar.write((addr & !0xff) | 0x8);
+        core.MPU.rbar.write((addr & !0xff) | (1 << 4)); // set address and update RNR
         core.MPU.rasr.write(
             1 // enable region
                | (0x7 << 1) // size 2^(7 + 1) = 256