diff --git a/Machines/Atari/ST/Video.cpp b/Machines/Atari/ST/Video.cpp
index a97d9b0ae..e0f01a5df 100644
--- a/Machines/Atari/ST/Video.cpp
+++ b/Machines/Atari/ST/Video.cpp
@@ -463,6 +463,8 @@ void Video::write(int address, uint16_t value) {
 		case 0x24:	case 0x25:	case 0x26:	case 0x27:
 		case 0x28:	case 0x29:	case 0x2a:	case 0x2b:
 		case 0x2c:	case 0x2d:	case 0x2e:	case 0x2f: {
+			if(address == 0x20) video_stream_.will_change_border_colour();
+
 			raw_palette_[address - 0x20] = value;
 			uint8_t *const entry = reinterpret_cast<uint8_t *>(&palette_[address - 0x20]);
 			entry[0] = uint8_t((value & 0x700) >> 7);
@@ -494,8 +496,8 @@ void Video::update_output_mode() {
 		video_stream_.set_bpp(output_bpp_);
 	}
 
-	const int freqs[] = {50, 60, 72};
-	printf("%d, %d -> %d [%d %d]\n", x_ / 2, y_, freqs[int(field_frequency_)], horizontal_.enable, vertical_.enable);
+//	const int freqs[] = {50, 60, 72};
+//	printf("%d, %d -> %d [%d %d]\n", x_ / 2, y_, freqs[int(field_frequency_)], horizontal_.enable, vertical_.enable);
 }
 
 // MARK: - The shifter
@@ -550,12 +552,6 @@ void Video::VideoStream::generate(int duration, OutputMode mode, bool is_termina
 		return;
 	}
 
-	// If the background colour has changed and border is accumulated, flush it.
-	if(border_colour_ != palette_[0] && duration_) {
-		flush_border();
-	}
-	border_colour_ = palette_[0];
-
 	// If the shifter is empty, accumulate in duration_ a promise to draw border later.
 	if(!output_shifter_) {
 		if(pixel_pointer_) {
@@ -586,10 +582,17 @@ void Video::VideoStream::generate(int duration, OutputMode mode, bool is_termina
 	}
 }
 
+void Video::VideoStream::will_change_border_colour() {
+	// Flush the accumulated border if it'd be adversely affected.
+	if(duration_ && output_mode_ == OutputMode::Pixels) {
+		flush_border();
+	}
+}
+
 void Video::VideoStream::flush_border() {
 	// Output colour 0 for the entirety of duration_ (or black, if this is 1bpp mode).
 	uint16_t *const colour_pointer = reinterpret_cast<uint16_t *>(crt_.begin_data(1));
-	if(colour_pointer) *colour_pointer = (bpp_ != OutputBpp::One) ?  border_colour_ : 0;
+	if(colour_pointer) *colour_pointer = (bpp_ != OutputBpp::One) ?  palette_[0] : 0;
 	crt_.output_level(duration_);
 
 	duration_ = 0;
diff --git a/Machines/Atari/ST/Video.hpp b/Machines/Atari/ST/Video.hpp
index f6345821d..ef4c3c19d 100644
--- a/Machines/Atari/ST/Video.hpp
+++ b/Machines/Atari/ST/Video.hpp
@@ -177,7 +177,6 @@ class Video {
 			public:
 				VideoStream(Outputs::CRT::CRT &crt, uint16_t *palette) : crt_(crt), palette_(palette) {}
 
-
 				enum class OutputMode {
 					Sync, Blank, ColourBurst, Pixels,
 				};
@@ -185,8 +184,14 @@ class Video {
 				/// Sets the current data format for the shifter. Changes in output BPP flush the shifter.
 				void set_bpp(OutputBpp bpp);
 
+				/// Outputs signal of type @c mode for @c duration.
 				void output(int duration, OutputMode mode);
 
+				/// Warns the video stream that the border colour, included in the palette that it holds a pointer to,
+				/// will change momentarily. This should be called after the relevant @c output() updates, and
+				/// is used to help elide border-regio output.
+				void will_change_border_colour();
+
 				/// Loads 64 bits into the Shifter. The shifter shifts continuously. If you also declare
 				/// a pixels region then whatever is being shifted will reach the display, in a form that
 				/// depends on the current output BPP.
@@ -208,7 +213,6 @@ class Video {
 				// Internal state that is a function of output intent.
 				int duration_ = 0;
 				OutputMode output_mode_ = OutputMode::Sync;
-				uint16_t border_colour_ = 0;
 				OutputBpp bpp_ = OutputBpp::Four;
 				union {
 					uint64_t output_shifter_;