diff --git a/runtime/src/interrupts.c b/runtime/src/interrupts.c
index 7279c045..b0e9dd7f 100644
--- a/runtime/src/interrupts.c
+++ b/runtime/src/interrupts.c
@@ -178,8 +178,8 @@ void psx_irq_raise(uint32_t bit, uint32_t detail)
 
 /* Dispatch counter for vblank scheduling. */
 #define VBLANK_INTERVAL 50000        /* legacy: dispatch-count fallback (unused for VBlank gating now) */
-#define VBLANK_CYCLES   564480u      /* 33.8688 MHz / 60 Hz — real PSX NTSC VBlank period */
-#define VBLANK_DEFER_STALE_CYCLES (VBLANK_CYCLES * 10ull)
+#define VBLANK_DEFER_STALE_CYCLES (vblank_cycles * 10ull)
+uint32_t vblank_cycles = 564480u;    /* 33.8688 MHz / 60 Hz — real PSX NTSC VBlank period */
 static uint32_t dispatch_count;
 static uint64_t total_checks;
 static uint32_t cycles_since_vblank;  /* incremented by interrupts_advance_cycles */
@@ -471,13 +471,13 @@ static void fire_vblank_edge(void) {
     /* Subtract one VBlank period rather than reset to 0 so cycle overshoot
      * carries forward. Prevents long-running blocks from rounding multiple
      * VBlanks together. */
-    cycles_since_vblank -= VBLANK_CYCLES;
+    cycles_since_vblank -= vblank_cycles;
     dispatch_count = 0;
     /* DEQUEUE: this VBlank fired. ENQUEUE: next VBlank scheduled one period out. */
     event_ring_record_aux(EV_DEQ, (uint8_t)SRC_VBLANK,
                           (uint32_t)psx_get_cycle_count());
     event_ring_record_aux(EV_ENQ, (uint8_t)SRC_VBLANK,
-                          (uint32_t)(psx_get_cycle_count() + VBLANK_CYCLES));
+                          (uint32_t)(psx_get_cycle_count() + vblank_cycles));
     psx_irq_raise(IRQ_VBLANK, 0);
     g_vblank_raise_count++;
     event_ring_record(EV_ISTAT_RAISE, IRQ_VBLANK);
@@ -493,15 +493,15 @@ static void fire_vblank_edge(void) {
 void interrupts_service_scheduled_events(void) {
     note_sio_progress_cycle();
     if (in_exception) return;
-    while (cycles_since_vblank >= VBLANK_CYCLES) {
+    while (cycles_since_vblank >= vblank_cycles) {
         if (should_defer_vblank_for_sio()) return;
         fire_vblank_edge();
     }
 }
 
 uint32_t interrupts_cycles_to_vblank(void) {
-    if (cycles_since_vblank >= VBLANK_CYCLES) return 0;
-    return VBLANK_CYCLES - cycles_since_vblank;
+    if (cycles_since_vblank >= vblank_cycles) return 0;
+    return vblank_cycles - cycles_since_vblank;
 }
 
 uint32_t interrupts_get_cycles_since_vblank(void) {
@@ -984,8 +984,8 @@ uint32_t cycles_to_next_event(void) {
      * card-SIO case only pushes VBlank LATER, so this estimate stays a safe
      * under-estimate. */
     if (i_mask & (1u << IRQ_VBLANK)) {
-        uint32_t d = (cycles_since_vblank >= VBLANK_CYCLES)
-                       ? 0u : (VBLANK_CYCLES - cycles_since_vblank);
+        uint32_t d = (cycles_since_vblank >= vblank_cycles)
+                       ? 0u : (vblank_cycles - cycles_since_vblank);
         if (d < best) best = d;
     }
     uint32_t t = timers_cycles_to_irq(i_mask); if (t < best) best = t;