diff --git a/ClockReceiver/JustInTime.hpp b/ClockReceiver/JustInTime.hpp
index 865f8ed53..610b04737 100644
--- a/ClockReceiver/JustInTime.hpp
+++ b/ClockReceiver/JustInTime.hpp
@@ -21,14 +21,18 @@
 	Machines that accumulate HalfCycle time but supply to a Cycle-counted device may supply a
 	separate @c TargetTimeScale at template declaration.
 */
-template <class T, int divider = 1, class LocalTimeScale = HalfCycles, class TargetTimeScale = LocalTimeScale> class JustInTimeActor {
+template <class T, int multiplier = 1, int divider = 1, class LocalTimeScale = HalfCycles, class TargetTimeScale = LocalTimeScale> class JustInTimeActor {
 	public:
 		/// Constructs a new JustInTimeActor using the same construction arguments as the included object.
 		template<typename... Args> JustInTimeActor(Args&&... args) : object_(std::forward<Args>(args)...) {}
 
 		/// Adds time to the actor.
 		inline void operator += (const LocalTimeScale &rhs) {
-			time_since_update_ += rhs;
+			if(multiplier != 1) {
+				time_since_update_ += rhs * multiplier;
+			} else {
+				time_since_update_ += rhs;
+			}
 			is_flushed_ = false;
 		}
 
diff --git a/Machines/Apple/Macintosh/Macintosh.cpp b/Machines/Apple/Macintosh/Macintosh.cpp
index 231b5f242..6f6daa9f0 100644
--- a/Machines/Apple/Macintosh/Macintosh.cpp
+++ b/Machines/Apple/Macintosh/Macintosh.cpp
@@ -656,7 +656,7 @@ template <Analyser::Static::Macintosh::Target::Model model> class ConcreteMachin
 			return mouse_;
 		}
 
-		using IWMActor = JustInTimeActor<IWM, 1, HalfCycles, Cycles>;
+		using IWMActor = JustInTimeActor<IWM, 1, 1, HalfCycles, Cycles>;
 
 		class VIAPortHandler: public MOS::MOS6522::PortHandler {
 			public:
diff --git a/Machines/AtariST/AtariST.cpp b/Machines/AtariST/AtariST.cpp
index 2cd49baf2..5eb927fab 100644
--- a/Machines/AtariST/AtariST.cpp
+++ b/Machines/AtariST/AtariST.cpp
@@ -32,7 +32,7 @@
 namespace Atari {
 namespace ST {
 
-const int CLOCK_RATE = 8000000;
+const int CLOCK_RATE = 8021247;
 
 /*!
 	A receiver for the Atari ST's "intelligent keyboard" commands, which actually cover
@@ -604,7 +604,8 @@ class ConcreteMachine:
 		JustInTimeActor<Video> video_;
 		HalfCycles cycles_until_video_event_;
 
-		JustInTimeActor<Motorola::MFP68901::MFP68901> mfp_;
+		// The MFP runs at 819200/2673749ths of the CPU clock rate.
+		JustInTimeActor<Motorola::MFP68901::MFP68901, 819200, 2673749> mfp_;
 		JustInTimeActor<Motorola::ACIA::ACIA, 16> keyboard_acia_;
 		JustInTimeActor<Motorola::ACIA::ACIA, 16> midi_acia_;
 
diff --git a/Machines/ColecoVision/ColecoVision.cpp b/Machines/ColecoVision/ColecoVision.cpp
index c2f347ec1..371cca534 100644
--- a/Machines/ColecoVision/ColecoVision.cpp
+++ b/Machines/ColecoVision/ColecoVision.cpp
@@ -397,7 +397,7 @@ class ConcreteMachine:
 		}
 
 		CPU::Z80::Processor<ConcreteMachine, false, false> z80_;
-		JustInTimeActor<TI::TMS::TMS9918, 1, HalfCycles> vdp_;
+		JustInTimeActor<TI::TMS::TMS9918, 1, 1, HalfCycles> vdp_;
 
 		Concurrency::DeferringAsyncTaskQueue audio_queue_;
 		TI::SN76489 sn76489_;