diff --git a/Machines/AmstradCPC/AmstradCPC.cpp b/Machines/AmstradCPC/AmstradCPC.cpp
index c570b341a..76d234613 100644
--- a/Machines/AmstradCPC/AmstradCPC.cpp
+++ b/Machines/AmstradCPC/AmstradCPC.cpp
@@ -222,9 +222,9 @@ class CRTCBusHandler {
 				if(cycles_) {
 					switch(previous_output_mode_) {
 						default:
-						case OutputMode::Blank:			crt_.output_blank(cycles_ * 16);					break;
+						case OutputMode::Blank:			crt_.output_blank(cycles_ * 16);				break;
 						case OutputMode::Sync:			crt_.output_sync(cycles_ * 16);					break;
-						case OutputMode::Border:		output_border(cycles_);								break;
+						case OutputMode::Border:		output_border(cycles_);							break;
 						case OutputMode::ColourBurst:	crt_.output_default_colour_burst(cycles_ * 16);	break;
 						case OutputMode::Pixels:
 							crt_.output_data(cycles_ * 16, size_t(cycles_ * 16 / pixel_divider_));
@@ -249,14 +249,16 @@ class CRTCBusHandler {
 					// the CPC shuffles output lines as:
 					//	MA13 MA12	RA2 RA1 RA0		MA9 MA8 MA7 MA6 MA5 MA4 MA3 MA2 MA1 MA0		CCLK
 					// ... so form the real access address.
-					uint16_t address =
+					const uint16_t address =
 						static_cast<uint16_t>(
 							((state.refresh_address & 0x3ff) << 1) |
 							((state.row_address & 0x7) << 11) |
 							((state.refresh_address & 0x3000) << 2)
 						);
 
-					// fetch two bytes and translate into pixels
+					// Fetch two bytes and translate into pixels. Guaranteed: the mode can change only at
+					// hsync, so there's no risk of pixel_pointer_ overrunning 320 output pixels without
+					// exactly reaching 320 output pixels.
 					switch(mode_) {
 						case 0:
 							reinterpret_cast<uint16_t *>(pixel_pointer_)[0] = mode0_output_[ram_[address]];
@@ -284,9 +286,9 @@ class CRTCBusHandler {
 
 					}
 
-					// flush the current buffer pixel if full; the CRTC allows many different display
+					// Flush the current buffer pixel if full; the CRTC allows many different display
 					// widths so it's not necessarily possible to predict the correct number in advance
-					// and using the upper bound could lead to inefficient behaviour
+					// and using the upper bound could lead to inefficient behaviour.
 					if(pixel_pointer_ == pixel_data_ + 320) {
 						crt_.output_data(cycles_ * 16, size_t(cycles_ * 16 / pixel_divider_));
 						pixel_pointer_ = pixel_data_ = nullptr;
@@ -369,9 +371,17 @@ class CRTCBusHandler {
 
 	private:
 		void output_border(int length) {
-			uint8_t *colour_pointer = static_cast<uint8_t *>(crt_.begin_data(1));
-			if(colour_pointer) *colour_pointer = border_;
-			crt_.output_level(length * 16);
+			assert(length >= 0);
+
+			// A black border can be output via crt_.output_blank for a minor performance
+			// win; otherwise paint whatever the border colour really is.
+			if(border_) {
+				uint8_t *const colour_pointer = static_cast<uint8_t *>(crt_.begin_data(1));
+				if(colour_pointer) *colour_pointer = border_;
+				crt_.output_level(length * 16);
+			} else {
+				crt_.output_blank(length * 16);
+			}
 		}
 
 #define Mode0Colour0(c) ((c & 0x80) >> 7) | ((c & 0x20) >> 3) | ((c & 0x08) >> 2) | ((c & 0x02) << 2)
diff --git a/Outputs/OpenGL/ScanTarget.hpp b/Outputs/OpenGL/ScanTarget.hpp
index ce7d671a7..cfe415ed3 100644
--- a/Outputs/OpenGL/ScanTarget.hpp
+++ b/Outputs/OpenGL/ScanTarget.hpp
@@ -123,8 +123,8 @@ class ScanTarget: public Outputs::Display::ScanTarget {
 		/// A pointer to the first thing not yet submitted for display.
 		std::atomic<PointerSet> read_pointers_;
 
-		// Maintains a buffer of the most recent 3072 scans.
-		std::array<Scan, 3072> scan_buffer_;
+		/// Maintains a buffer of the most recent scans.
+		std::array<Scan, 16384> scan_buffer_;
 
 		// Maintains a list of composite scan buffer coordinates; the Line struct
 		// is transported to the GPU in its entirety; the LineMetadatas live in CPU