diff --git a/arch/arm/core/exc_exit.S b/arch/arm/core/exc_exit.S
index c8e8250b629..64bf2ef4771 100644
--- a/arch/arm/core/exc_exit.S
+++ b/arch/arm/core/exc_exit.S
@@ -103,6 +103,28 @@ SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _ExcExit)
     bgt _EXIT_EXC
 
     push {lr}
+
+    /*
+     * _is_next_thread_current() calls _get_next_ready_thread(), which is
+     * supposed to be called only with interrupts locked: interrupts are _not_
+     * locked at this point. However, that is not a problem in this case:
+     *
+     * - Threads can only be added to the ready queue in an ISR, not removed.
+     *   Thus, priorities with runnable thread can only be added as well.
+     *
+     * - The PendSV handler is the context that will decide which thread to
+     *   run, not the current context.
+     *
+     * - The current decision to pend PendSV or not is started with the ready
+     *   queue state that the currently exiting ISR updated: if that state
+     *   changes, it can only be to add a thread as runnable, not remove one.
+     *
+     * - The only discrepancy that can happen is if another ISR preempts the
+     *   current one and makes another thread than the current the next thread
+     *   to run, if the current ISR did not do already that. In that case, even
+     *   if the decision is interrupted, the current code running in the higher
+     *   priority ISR _will_ take the correct decision to pend PendSV.
+     */
     blx _is_next_thread_current
 #if defined(CONFIG_CPU_CORTEX_M0_M0PLUS)
     pop {r1}