diff --git a/CHANGES b/CHANGES
index 6661f12bc..8095d4625 100644
--- a/CHANGES
+++ b/CHANGES
@@ -10,6 +10,7 @@ Bugfixes:
  - LR35902: Fix events running with the wrong cycle active
  - GB Video: Clear screen when LCDC is off
  - GBA Cheats: Fix key-activated CodeBreaker cheats
+ - GB SIO: Don't auto-clock external shift clock
 Misc:
  - All: Only update version info if needed
  - FFmpeg: Encoding cleanup
diff --git a/src/gb/sio.c b/src/gb/sio.c
index 7e114b2e9..035b3a42e 100644
--- a/src/gb/sio.c
+++ b/src/gb/sio.c
@@ -46,7 +46,9 @@ int32_t GBSIOProcessEvents(struct GBSIO* sio, int32_t cycles) {
 void GBSIOWriteSC(struct GBSIO* sio, uint8_t sc) {
 	sio->period = 0x1000; // TODO Shift Clock
 	if (GBRegisterSCIsEnable(sc)) {
-		sio->nextEvent = sio->p->cpu->cycles + sio->period;
+		if (GBRegisterSCIsShiftClock(sc)) {
+			sio->nextEvent = sio->p->cpu->cycles + sio->period;
+		}
 		sio->remainingBits = 8;
 	}
 }