diff --git a/CHANGES b/CHANGES
index 970a83ae5..bbca29273 100644
--- a/CHANGES
+++ b/CHANGES
@@ -18,6 +18,7 @@ Bugfixes:
  - Qt: Fix timezone issues with time overrides
  - Qt: Fix sprite export pausing game indefinitely (fixes mgba.io/i/841)
  - GB Video: Fix potential hang when ending mode 0
+ - GB Memory: Fix HDMA count starting in mode 0 (fixes mgba.io/i/855)
 Misc:
  - Qt: Don't rebuild library view if style hasn't changed
  - SDL: Fix 2.0.5 build on macOS under some circumstances
diff --git a/src/gb/memory.c b/src/gb/memory.c
index e593d6b23..21c9e17a3 100644
--- a/src/gb/memory.c
+++ b/src/gb/memory.c
@@ -464,10 +464,13 @@ void GBMemoryWriteHDMA5(struct GB* gb, uint8_t value) {
 	bool wasHdma = gb->memory.isHdma;
 	gb->memory.isHdma = value & 0x80;
 	if ((!wasHdma && !gb->memory.isHdma) || gb->video.mode == 0) {
-		gb->memory.hdmaRemaining = ((value & 0x7F) + 1) * 0x10;
+		if (gb->memory.isHdma) {
+			gb->memory.hdmaRemaining = 0x10;
+		} else {
+			gb->memory.hdmaRemaining = ((value & 0x7F) + 1) * 0x10;
+		}
 		gb->cpuBlocked = true;
 		mTimingSchedule(&gb->timing, &gb->memory.hdmaEvent, 0);
-		gb->cpu->nextEvent = gb->cpu->cycles;
 	}
 }
 
diff --git a/src/gb/video.c b/src/gb/video.c
index 6fda8c5e4..49bbff1f8 100644
--- a/src/gb/video.c
+++ b/src/gb/video.c
@@ -231,6 +231,7 @@ void _endMode3(struct mTiming* timing, void* context, uint32_t cyclesLate) {
 	GBVideoProcessDots(video);
 	if (video->ly < GB_VIDEO_VERTICAL_PIXELS && video->p->memory.isHdma && video->p->memory.io[REG_HDMA5] != 0xFF) {
 		video->p->memory.hdmaRemaining = 0x10;
+		video->p->cpuBlocked = true;
 		mTimingDeschedule(timing, &video->p->memory.hdmaEvent);
 		mTimingSchedule(timing, &video->p->memory.hdmaEvent, 0);
 	}