diff --git a/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal b/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal
index 7bc5f57ef..cab2225de 100644
--- a/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal	
+++ b/OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal	
@@ -60,7 +60,8 @@ constexpr sampler linearSampler(	coord::pixel,
 
 // MARK: - Structs used for receiving data from the emulation.
 
-// This is intended to match the net effect of `Scan` as defined by the BufferingScanTarget.
+// This is intended to match the net effect of `Scan` as defined by the BufferingScanTarget,
+// with a couple of added fields.
 struct Scan {
 	struct EndPoint {
 		uint16_t position[2];
@@ -69,7 +70,10 @@ struct Scan {
 		uint16_t cyclesSinceRetrace;
 	} endPoints[2];
 
-	uint8_t compositeAmplitude;
+	union {
+		uint8_t compositeAmplitude;
+		uint32_t padding;			// TODO: reuse some padding as the next two fields, to save two bytes.
+	};
 	uint16_t dataY;
 	uint16_t line;
 };
diff --git a/Outputs/OpenGL/ScanTargetGLSLFragments.cpp b/Outputs/OpenGL/ScanTargetGLSLFragments.cpp
index 0404f95e8..bdfd5649a 100644
--- a/Outputs/OpenGL/ScanTargetGLSLFragments.cpp
+++ b/Outputs/OpenGL/ScanTargetGLSLFragments.cpp
@@ -84,6 +84,11 @@ void ScanTarget::enable_vertex_attributes(ShaderType type, Shader &target) {
 	Scan test_scan;
 	Line test_line;
 
+	// Some GPUs require alignment and will need to copy vertex data to a
+	// shadow buffer otherwise
+	static_assert(sizeof(Scan) % 4 == 0);
+	static_assert(sizeof(Line) % 4 == 0);
+
 	switch(type) {
 		case ShaderType::Composition:
 			for(int c = 0; c < 2; ++c) {
diff --git a/Outputs/ScanTarget.hpp b/Outputs/ScanTarget.hpp
index dc4074d95..0a32ac346 100644
--- a/Outputs/ScanTarget.hpp
+++ b/Outputs/ScanTarget.hpp
@@ -304,7 +304,11 @@ struct ScanTarget {
 
 			/// For composite video, dictates the amplitude of the colour subcarrier as a proportion of
 			/// the whole, as determined from the colour burst. Will be 0 if there was no colour burst.
-			uint8_t composite_amplitude;
+			union {
+				uint8_t composite_amplitude;
+
+				uint32_t padding;
+			};
 		};
 
 		/// Requests a new scan to populate.