diff --git a/tests/amtest/src/tests/extintr.c b/tests/amtest/src/tests/extintr.c
index 471d663d31711f835eb16e9d3b4c63b978e60f9a..ef9d322b68bfcc40401c2861a9b7ef874722746d 100644
--- a/tests/amtest/src/tests/extintr.c
+++ b/tests/amtest/src/tests/extintr.c
@@ -168,7 +168,8 @@ void random_trigger() {
   for (int i = 0; i < (MAX_EXTERNAL_INTR + 31) / 32; i++) {
     WRITE_WORD(INTR_RANDOM_ADDR(i), 0xffffffff);
   }
-  for (int i = 0; i < (MAX_EXTERNAL_INTR + 31) / 32; i++) {
+  // Add one here because PLIC interrupt number starts at 1.
+  for (int i = 0; i < (MAX_EXTERNAL_INTR + 1 + 31) / 32; i++) {
     WRITE_WORD(PLIC_ENABLE(CONTEXT_S) + i * 4, 0xffffffff);
   }
   void hello_intr_n(int n);