diff --git a/GPU/Common/DrawEngineCommon.cpp b/GPU/Common/DrawEngineCommon.cpp
index 495b206515..46742e79b7 100644
--- a/GPU/Common/DrawEngineCommon.cpp
+++ b/GPU/Common/DrawEngineCommon.cpp
@@ -244,7 +244,7 @@ void DrawEngineCommon::DispatchSubmitImm(GEPrimitiveType prim, TransformedVertex
 //
 // It does the simplest and safest test possible: If all points of a bbox is outside a single of
 // our clipping planes, we reject the box. Tighter bounds would be desirable but would take more calculations.
-bool DrawEngineCommon::TestBoundingBox(const void* control_points, int vertexCount, u32 vertType, int *bytesRead) {
+bool DrawEngineCommon::TestBoundingBox(const void* control_points, int vertexCount, u32 vertType) {
 	SimpleVertex *corners = (SimpleVertex *)(decoded + 65536 * 12);
 	float *verts = (float *)(decoded + 65536 * 18);
 
@@ -252,19 +252,16 @@ bool DrawEngineCommon::TestBoundingBox(const void* control_points, int vertexCou
 	// and a large vertex format.
 	if ((vertType & 0xFFFFFF) == GE_VTYPE_POS_FLOAT) {
 		verts = (float *)control_points;
-		*bytesRead = 3 * sizeof(float) * vertexCount;
 	} else if ((vertType & 0xFFFFFF) == GE_VTYPE_POS_8BIT) {
 		const s8 *vtx = (const s8 *)control_points;
 		for (int i = 0; i < vertexCount * 3; i++) {
 			verts[i] = vtx[i] * (1.0f / 128.0f);
 		}
-		*bytesRead = 3 * sizeof(s8) * vertexCount;
 	} else if ((vertType & 0xFFFFFF) == GE_VTYPE_POS_16BIT) {
 		const s16 *vtx = (const s16*)control_points;
 		for (int i = 0; i < vertexCount * 3; i++) {
 			verts[i] = vtx[i] * (1.0f / 32768.0f);
 		}
-		*bytesRead = 3 * sizeof(s16) * vertexCount;
 	} else {
 		// Simplify away bones and morph before proceeding
 		u8 *temp_buffer = decoded + 65536 * 24;
@@ -275,7 +272,6 @@ bool DrawEngineCommon::TestBoundingBox(const void* control_points, int vertexCou
 			verts[i * 3 + 1] = corners[i].pos.y;
 			verts[i * 3 + 2] = corners[i].pos.z;
 		}
-		*bytesRead = vertexSize * vertexCount;
 	}
 
 	Plane planes[6];
diff --git a/GPU/Common/DrawEngineCommon.h b/GPU/Common/DrawEngineCommon.h
index 8fc0382a29..7a6ba863fd 100644
--- a/GPU/Common/DrawEngineCommon.h
+++ b/GPU/Common/DrawEngineCommon.h
@@ -92,7 +92,7 @@ public:
 
 	virtual void DispatchSubmitImm(GEPrimitiveType prim, TransformedVertex *buffer, int vertexCount, int cullMode, bool continuation);
 
-	bool TestBoundingBox(const void* control_points, int vertexCount, u32 vertType, int *bytesRead);
+	bool TestBoundingBox(const void* control_points, int vertexCount, u32 vertType);
 
 	void SubmitPrim(const void *verts, const void *inds, GEPrimitiveType prim, int vertexCount, u32 vertTypeID, int cullMode, int *bytesRead);
 	template<class Surface>
diff --git a/GPU/GPUCommon.cpp b/GPU/GPUCommon.cpp
index 7a6b3fea88..35d91df78a 100644
--- a/GPU/GPUCommon.cpp
+++ b/GPU/GPUCommon.cpp
@@ -2153,13 +2153,17 @@ void GPUCommon::Execute_Spline(u32 op, u32 diff) {
 
 void GPUCommon::Execute_BoundingBox(u32 op, u32 diff) {
 	// Just resetting, nothing to check bounds for.
-	const u32 count = op & 0xFFFFFF;
+	const u32 count = op & 0xFFFF;
 	if (count == 0) {
 		currentList->bboxResult = false;
 		return;
 	}
-	if (((count & 7) == 0) && count <= 64) {  // Sanity check
-		const void *control_points = Memory::GetPointer(gstate_c.vertexAddr);
+
+	VertexDecoder *dec = drawEngineCommon_->GetVertexDecoder(gstate.vertType);
+	int bytesRead = dec->VertexSize() * count;
+
+	if (Memory::IsValidRange(gstate_c.vertexAddr, bytesRead)) {
+		const void *control_points = Memory::GetPointerUnchecked(gstate_c.vertexAddr);
 		if (!control_points) {
 			ERROR_LOG_REPORT_ONCE(boundingbox, G3D, "Invalid verts in bounding box check");
 			currentList->bboxResult = true;
@@ -2174,8 +2178,17 @@ void GPUCommon::Execute_BoundingBox(u32 op, u32 diff) {
 		}
 
 		// Test if the bounding box is within the drawing region.
-		int bytesRead;
-		currentList->bboxResult = drawEngineCommon_->TestBoundingBox(control_points, count, gstate.vertType, &bytesRead);
+		// The PSP only seems to vary the result based on a single range of 0x100.
+		if (count > 0x200) {
+			// The second to last set of 0x100 is checked (even for odd counts.)
+			size_t skipSize = (count - 0x200) * dec->VertexSize();
+			currentList->bboxResult = drawEngineCommon_->TestBoundingBox((const uint8_t *)control_points + skipSize, 0x100, gstate.vertType);
+		} else if (count > 0x100) {
+			int checkSize = count - 0x100;
+			currentList->bboxResult = drawEngineCommon_->TestBoundingBox(control_points, checkSize, gstate.vertType);
+		} else {
+			currentList->bboxResult = drawEngineCommon_->TestBoundingBox(control_points, count, gstate.vertType);
+		}
 		AdvanceVerts(gstate.vertType, count, bytesRead);
 	} else {
 		ERROR_LOG_REPORT_ONCE(boundingbox, G3D, "Bad bounding box data: %06x", count);