diff --git a/OSBindings/Mac/Clock Signal/Base.lproj/MainMenu.xib b/OSBindings/Mac/Clock Signal/Base.lproj/MainMenu.xib
index ff476331c..e617f15ca 100644
--- a/OSBindings/Mac/Clock Signal/Base.lproj/MainMenu.xib	
+++ b/OSBindings/Mac/Clock Signal/Base.lproj/MainMenu.xib	
@@ -111,6 +111,12 @@
                                 </connections>
                             </menuItem>
                             <menuItem isSeparatorItem="YES" id="aJh-i4-bef"/>
+                            <menuItem title="Save Screenshot" keyEquivalent="D" id="BVJ-oQ-hUp">
+                                <connections>
+                                    <action selector="saveScreenshot:" target="-1" id="7ky-xD-tip"/>
+                                </connections>
+                            </menuItem>
+                            <menuItem isSeparatorItem="YES" id="rXU-KX-GkZ"/>
                             <menuItem title="Page Setup…" enabled="NO" keyEquivalent="P" id="qIS-W8-SiK">
                                 <modifierMask key="keyEquivalentModifierMask" shift="YES" command="YES"/>
                                 <connections>
diff --git a/OSBindings/Mac/Clock Signal/Clock Signal.entitlements b/OSBindings/Mac/Clock Signal/Clock Signal.entitlements
index 74600409e..d6593673f 100644
--- a/OSBindings/Mac/Clock Signal/Clock Signal.entitlements	
+++ b/OSBindings/Mac/Clock Signal/Clock Signal.entitlements	
@@ -4,6 +4,8 @@
 <dict>
 	<key>com.apple.security.app-sandbox</key>
 	<true/>
+	<key>com.apple.security.assets.pictures.read-write</key>
+	<true/>
 	<key>com.apple.security.device.bluetooth</key>
 	<true/>
 	<key>com.apple.security.device.usb</key>
diff --git a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift
index f5137594d..1c26fbd5b 100644
--- a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
+++ b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
@@ -6,8 +6,8 @@
 //  Copyright 2016 Thomas Harte. All rights reserved.
 //
 
-import Cocoa
 import AudioToolbox
+import Cocoa
 
 class MachineDocument:
 	NSDocument,
@@ -310,6 +310,29 @@ class MachineDocument:
 		return super.validateUserInterfaceItem(item)
 	}
 
+	// Screenshot capture.
+	@IBAction func saveScreenshot(_ sender: AnyObject!) {
+		// Grab a date formatter and form a file name.
+		let dateFormatter = DateFormatter()
+		dateFormatter.dateStyle = .short
+		dateFormatter.timeStyle = .long
+
+		let filename = ("Clock Signal Screen Shot " + dateFormatter.string(from: Date()) + ".png").replacingOccurrences(of: "/", with: "-")
+			.replacingOccurrences(of: ":", with: ".")
+		let pictursURL = FileManager.default.urls(for: .picturesDirectory, in: .userDomainMask)[0]
+		let url = pictursURL.appendingPathComponent(filename)
+
+		// Obtain the machine's current display.
+		var imageRepresentation: NSBitmapImageRep? = nil
+		self.openGLView.perform {
+			imageRepresentation = self.machine.imageRepresentation
+		}
+
+		// Encode as a PNG and save.
+		let pngData = imageRepresentation!.representation(using: .png, properties: [:])
+		try! pngData?.write(to: url)
+	}
+
 	// MARK: Activity display.
 	class LED {
 		let levelIndicator: NSLevelIndicator
diff --git a/OSBindings/Mac/Clock Signal/Machine/CSMachine.h b/OSBindings/Mac/Clock Signal/Machine/CSMachine.h
index 458a0b5cc..8934d88f3 100644
--- a/OSBindings/Mac/Clock Signal/Machine/CSMachine.h	
+++ b/OSBindings/Mac/Clock Signal/Machine/CSMachine.h	
@@ -64,6 +64,7 @@ typedef NS_ENUM(NSInteger, CSMachineKeyboardInputMode) {
 @property (nonatomic, readonly, nonnull) NSString *userDefaultsPrefix;
 
 - (void)paste:(nonnull NSString *)string;
+@property (nonatomic, readonly, nonnull) NSBitmapImageRep *imageRepresentation;
 
 @property (nonatomic, assign) BOOL useFastLoadingHack;
 @property (nonatomic, assign) CSMachineVideoSignal videoSignal;
diff --git a/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm b/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm
index 117b86718..a219a1801 100644
--- a/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm	
+++ b/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm	
@@ -243,6 +243,43 @@ struct ActivityObserver: public Activity::Observer {
 		keyboardMachine->type_string([paste UTF8String]);
 }
 
+- (NSBitmapImageRep *)imageRepresentation {
+	// Get the current viewport to establish framebuffer size. Then determine how wide the
+	// centre 4/3 of that would be.
+	GLint dimensions[4];
+	glGetIntegerv(GL_VIEWPORT, dimensions);
+	GLint proportionalWidth = (dimensions[3] * 4) / 3;
+
+	// Grab the framebuffer contents.
+	std::vector<uint8_t> temporaryData(static_cast<size_t>(proportionalWidth * dimensions[3] * 3));
+	glReadPixels((dimensions[2] - proportionalWidth) >> 1, 0, proportionalWidth, dimensions[3], GL_RGB, GL_UNSIGNED_BYTE, temporaryData.data());
+
+	// Generate an NSBitmapImageRep and populate it with a vertical flip
+	// of the original data.
+	NSBitmapImageRep *const result =
+		[[NSBitmapImageRep alloc]
+			initWithBitmapDataPlanes:NULL
+			pixelsWide:proportionalWidth
+			pixelsHigh:dimensions[3]
+			bitsPerSample:8
+			samplesPerPixel:3
+			hasAlpha:NO
+			isPlanar:NO
+			colorSpaceName:NSDeviceRGBColorSpace
+			bytesPerRow:3 * proportionalWidth
+			bitsPerPixel:0];
+
+	const size_t line_size = static_cast<size_t>(proportionalWidth * 3);
+	for(GLint y = 0; y < dimensions[3]; ++y) {
+		memcpy(
+			&result.bitmapData[static_cast<size_t>(y) * line_size],
+			&temporaryData[static_cast<size_t>(dimensions[3] - y - 1) * line_size],
+			line_size);
+	}
+
+	return result;
+}
+
 - (void)applyMedia:(const Analyser::Static::Media &)media {
 	@synchronized(self) {
 		MediaTarget::Machine *const mediaTarget = _machine->media_target();
diff --git a/OSBindings/SDL/main.cpp b/OSBindings/SDL/main.cpp
index 299474e53..c08d4507c 100644
--- a/OSBindings/SDL/main.cpp
+++ b/OSBindings/SDL/main.cpp
@@ -632,7 +632,16 @@ int main(int argc, char *argv[]) {
 						}
 
 						// Create a suitable SDL surface and save the thing.
-						SDL_Surface *const surface = SDL_CreateRGBSurfaceFrom(pixels.data(), proportional_width, window_height, 8*4, proportional_width*4, 0, 0, 0, 0);
+						const bool is_big_endian = SDL_BYTEORDER == SDL_BIG_ENDIAN;
+						SDL_Surface *const surface = SDL_CreateRGBSurfaceFrom(
+							pixels.data(),
+							proportional_width, window_height,
+							8*4,
+							proportional_width*4,
+							is_big_endian ? 0xff000000 : 0x000000ff,
+							is_big_endian ? 0x00ff0000 : 0x0000ff00,
+							is_big_endian ? 0x0000ff00 : 0x00ff0000,
+							0);
 						SDL_SaveBMP(surface, target.c_str());
 						SDL_FreeSurface(surface);
 						break;