diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 2db82661cd60..a3aa5e5b039d 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -290,8 +290,9 @@ should_watch(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int t
 }
 
 /*
- * Returns a pseudo-random number in interval [0, ep_ro). Simple linear
- * congruential generator, using constants from "Numerical Recipes".
+ * Returns a pseudo-random number in interval [0, ep_ro), or 0 if ep_ro is 0,
+ * which the runtime-tunable callers may pass. Simple linear congruential
+ * generator, using constants from "Numerical Recipes".
  */
 static u32 kcsan_prandom_u32_max(u32 ep_ro)
 {
@@ -300,7 +301,7 @@ static u32 kcsan_prandom_u32_max(u32 ep_ro)
 	state = 1664525 * state + 1013904223;
 	this_cpu_write(kcsan_rand_state, state);
 
-	return state % ep_ro;
+	return reciprocal_scale(state, ep_ro);
 }
 
 static inline void reset_kcsan_skip(void)