diff --git a/Machines/Apple/AppleII/AppleII.cpp b/Machines/Apple/AppleII/AppleII.cpp
index 25898655f..3757092e1 100644
--- a/Machines/Apple/AppleII/AppleII.cpp
+++ b/Machines/Apple/AppleII/AppleII.cpp
@@ -84,8 +84,10 @@ template <Analyser::Static::AppleII::Target::Model model> class ConcreteMachine:
 			speaker_.run_for(audio_queue_, cycles_since_audio_update_.divide(Cycles(audio_divider)));
 		}
 		void update_just_in_time_cards() {
-			for(const auto &card : just_in_time_cards_) {
-				card->run_for(cycles_since_card_update_, stretched_cycles_since_card_update_);
+			if(cycles_since_card_update_ > Cycles(0)) {
+				for(const auto &card : just_in_time_cards_) {
+					card->run_for(cycles_since_card_update_, stretched_cycles_since_card_update_);
+				}
 			}
 			cycles_since_card_update_ = 0;
 			stretched_cycles_since_card_update_ = 0;
@@ -124,19 +126,25 @@ template <Analyser::Static::AppleII::Target::Model model> class ConcreteMachine:
 			pick_card_messaging_group(card);
 		}
 
-		bool is_every_cycle_card(Apple::II::Card *card) {
+		bool is_every_cycle_card(const Apple::II::Card *card) {
 			return !card->get_select_constraints();
 		}
 
+		bool card_lists_are_dirty_ = true;
+		bool card_became_just_in_time_ = false;
 		void pick_card_messaging_group(Apple::II::Card *card) {
+			// Simplify to a card being either just-in-time or realtime.
+			// Don't worry about exactly what it's watching,
 			const bool is_every_cycle = is_every_cycle_card(card);
 			std::vector<Apple::II::Card *> &intended = is_every_cycle ? every_cycle_cards_ : just_in_time_cards_;
-			std::vector<Apple::II::Card *> &undesired = is_every_cycle ? just_in_time_cards_ : every_cycle_cards_;
 
+			// If the card is already in the proper group, stop.
 			if(std::find(intended.begin(), intended.end(), card) != intended.end()) return;
-			auto old_membership = std::find(undesired.begin(), undesired.end(), card);
-			if(old_membership != undesired.end()) undesired.erase(old_membership);
-			intended.push_back(card);
+
+			// Otherwise, mark the sets as dirty. It isn't safe to transition the card here,
+			// as the main loop may be part way through iterating the two lists.
+			card_lists_are_dirty_ = true;
+			card_became_just_in_time_ |= !is_every_cycle;
 		}
 
 		void card_did_change_select_constraints(Apple::II::Card *card) override {
@@ -753,6 +761,31 @@ template <Analyser::Static::AppleII::Target::Model model> class ConcreteMachine:
 				}
 			}
 
+			// Update the card lists if any mutations are due.
+			if(card_lists_are_dirty_) {
+				card_lists_are_dirty_ = false;
+
+				// There's only one counter of time since update
+				// for just-in-time cards. If something new is
+				// transitioning, that needs to be zeroed.
+				if(card_became_just_in_time_) {
+					card_became_just_in_time_ = false;
+					update_just_in_time_cards();
+				}
+
+				// Clear the two lists and repopulate.
+				every_cycle_cards_.clear();
+				just_in_time_cards_.clear();
+				for(const auto &card: cards_) {
+					if(!card) continue;
+					if(is_every_cycle_card(card.get())) {
+						every_cycle_cards_.push_back(card.get());
+					} else {
+						just_in_time_cards_.push_back(card.get());
+					}
+				}
+			}
+
 			// Update analogue charge level.
 			analogue_charge_ = std::min(analogue_charge_ + 1.0f / 2820.0f, 1.1f);
 
diff --git a/Machines/Apple/AppleII/Card.hpp b/Machines/Apple/AppleII/Card.hpp
index 7e68daf81..7db80b39e 100644
--- a/Machines/Apple/AppleII/Card.hpp
+++ b/Machines/Apple/AppleII/Card.hpp
@@ -83,10 +83,8 @@ class Card {
 			will receive a perform_bus_operation every cycle. To reduce the number of
 			virtual method calls, they **will not** receive run_for. run_for will propagate
 			only to cards that register for IO and/or Device accesses only.
-
-
 		*/
-		int get_select_constraints() {
+		int get_select_constraints() const {
 			return select_constraints_;
 		}
 
diff --git a/Machines/Apple/AppleII/DiskIICard.cpp b/Machines/Apple/AppleII/DiskIICard.cpp
index 11349e1fc..a5c721bb7 100644
--- a/Machines/Apple/AppleII/DiskIICard.cpp
+++ b/Machines/Apple/AppleII/DiskIICard.cpp
@@ -65,7 +65,7 @@ void DiskIICard::set_activity_observer(Activity::Observer *observer) {
 
 void DiskIICard::set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference preference) {
 	diskii_clocking_preference_ = preference;
-	set_select_constraints((preference != ClockingHint::Preference::RealTime) ? (IO | Device) : 0);
+	set_select_constraints((preference != ClockingHint::Preference::RealTime) ? (IO | Device) : None);
 }
 
 Storage::Disk::Drive &DiskIICard::get_drive(int drive) {
diff --git a/Storage/Disk/Drive.cpp b/Storage/Disk/Drive.cpp
index 8a702b568..e0068ba5d 100644
--- a/Storage/Disk/Drive.cpp
+++ b/Storage/Disk/Drive.cpp
@@ -20,8 +20,8 @@ using namespace Storage::Disk;
 
 Drive::Drive(int input_clock_rate, int revolutions_per_minute, int number_of_heads):
 	Storage::TimedEventLoop(input_clock_rate),
-	rotational_multiplier_(60.0f / float(revolutions_per_minute)),
 	available_heads_(number_of_heads) {
+	set_rotation_speed(revolutions_per_minute);
 
 	const auto seed = static_cast<std::default_random_engine::result_type>(std::chrono::system_clock::now().time_since_epoch().count());
 	std::default_random_engine randomiser(seed);