diff --git a/GPU/Common/FramebufferCommon.cpp b/GPU/Common/FramebufferCommon.cpp
index 373bdc557f..086317c5be 100644
--- a/GPU/Common/FramebufferCommon.cpp
+++ b/GPU/Common/FramebufferCommon.cpp
@@ -152,8 +152,9 @@ bool FramebufferManagerCommon::ShouldDownloadFramebuffer(const VirtualFramebuffe
 // Heuristics to figure out the size of FBO to create.
 void FramebufferManagerCommon::EstimateDrawingSize(int &drawing_width, int &drawing_height) {
 	static const int MAX_FRAMEBUF_HEIGHT = 512;
-	const int viewport_width = (int) gstate.getViewportX1();
-	const int viewport_height = (int) gstate.getViewportY1();
+	// Viewport-X1 and Y1 are not the upper left corner, but half the width/height. A bit confusing.
+	const int viewport_width = (int)(fabsf(gstate.getViewportX1()*2.0f));
+	const int viewport_height = (int)(fabsf(gstate.getViewportY1()*2.0f));
 	const int region_width = gstate.getRegionX2() + 1;
 	const int region_height = gstate.getRegionY2() + 1;
 	const int scissor_width = gstate.getScissorX2() + 1;
diff --git a/GPU/GPUState.h b/GPU/GPUState.h
index 6c27467386..0e1f68f739 100644
--- a/GPU/GPUState.h
+++ b/GPU/GPUState.h
@@ -392,12 +392,15 @@ struct GPUgstate
 	int getRegionY1() const { return (region1 >> 10) & 0x3FF; }
 	int getRegionX2() const { return (region2 & 0x3FF); }
 	int getRegionY2() const { return (region2 >> 10) & 0x3FF; }
+
+	// Note that the X1/Y1/Z1 here does not mean the upper-left corner, but half the dimensions. X2/Y2/Z2 are the center.
 	float getViewportX1() const { return getFloat24(viewportx1); }
 	float getViewportY1() const { return getFloat24(viewporty1); }
 	float getViewportZ1() const { return getFloat24(viewportz1); }
 	float getViewportX2() const { return getFloat24(viewportx2); }
 	float getViewportY2() const { return getFloat24(viewporty2); }
 	float getViewportZ2() const { return getFloat24(viewportz2); }
+
 	// Fixed 16 point.
 	int getOffsetX16() const { return offsetx & 0xFFFF; }
 	// Fixed 16 point.
diff --git a/headless/Compare.cpp b/headless/Compare.cpp
index 607816aac4..446546df81 100644
--- a/headless/Compare.cpp
+++ b/headless/Compare.cpp
@@ -20,6 +20,8 @@
 
 #include "Common/ColorConv.h"
 #include "Core/Host.h"
+
+#include "GPU/GPUState.h"
 #include "GPU/Common/GPUDebugInterface.h"
 #include "GPU/Common/TextureDecoder.h"