diff --git a/Machines/AmstradCPC/AmstradCPC.cpp b/Machines/AmstradCPC/AmstradCPC.cpp
index 796d7b4e8..469473243 100644
--- a/Machines/AmstradCPC/AmstradCPC.cpp
+++ b/Machines/AmstradCPC/AmstradCPC.cpp
@@ -30,9 +30,9 @@ class InterruptTimer {
 		InterruptTimer() : timer_(0), interrupt_request_(false) {}
 
 		/*!
-			Indicates that a new hsync pulse has been recognised. Per documentation
-			difficulties, it is not presently clear to me whether this should be
-			the leading or trailing edge of horizontal sync.
+			Indicates that a new hsync pulse has been recognised. This should be
+			supplied on the falling edge of the CRTC HSYNC signal, which is the
+			trailing edge because it is active high.
 		*/
 		inline void signal_hsync() {
 			// Increment the timer and if it has hit 52 then reset it and
@@ -49,7 +49,7 @@ class InterruptTimer {
 			if(reset_counter_) {
 				reset_counter_--;
 				if(!reset_counter_) {
-					if(timer_ < 32) {
+					if(timer_ & 32) {
 						interrupt_request_ = true;
 					}
 					timer_ = 0;
@@ -76,6 +76,7 @@ class InterruptTimer {
 		/// Resets the timer.
 		inline void reset_count() {
 			timer_ = 0;
+			interrupt_request_ = false;
 		}
 
 	private: