diff --git a/src/devices/imagedev/floppy.cpp b/src/devices/imagedev/floppy.cpp
index 6d87751280e..bba469c9d93 100644
--- a/src/devices/imagedev/floppy.cpp
+++ b/src/devices/imagedev/floppy.cpp
@@ -932,9 +932,7 @@ attotime floppy_image_device::get_next_transition(const attotime &from_when)
 		return cache_end_time;
 
 	// Put a flux transition in the middle of a 4us interval with a 50% probability
-	int64_t interval_index = (from_when - cache_weak_start).as_ticks(250000);
-	if(interval_index < 0)
-		interval_index = 0;
+	uint64_t interval_index = (from_when < cache_weak_start) ? 0 : (from_when - cache_weak_start).as_ticks(250000);
 	attotime weak_time = cache_weak_start + attotime::from_ticks(interval_index*2+1, 500000);
 	for(;;) {
 		if(weak_time >= cache_end_time)