diff --git a/libweston/vertex-clipping.c b/libweston/vertex-clipping.c
index 7f659e189..4de172e4e 100644
--- a/libweston/vertex-clipping.c
+++ b/libweston/vertex-clipping.c
@@ -374,7 +374,7 @@ clipper_quad_clip(struct clipper_quad *quad,
 			vertices[i].y = CLIP(quad->polygon[i].y,
 					     box[0].y, box[1].y);
 		}
-		if ((vertices[0].x != vertices[1].x) &&
+		if ((vertices[0].x != vertices[2].x) &&
 		    (vertices[0].y != vertices[2].y))
 			return 4;
 		else
diff --git a/tests/vertex-clip-test.c b/tests/vertex-clip-test.c
index 543143eb7..0c0be6769 100644
--- a/tests/vertex-clip-test.c
+++ b/tests/vertex-clip-test.c
@@ -583,17 +583,99 @@ static const struct vertex_clip_test_data quad_clip_expected_data[] = {
 		.clipped_n = 5,
 	},
 
-	/* Miscellaneous cases: */
+	/* Box intersects entire smaller aligned quad of different winding
+	 * orders and first edge orientations: */
 
-	/* Box intersects entire smaller aligned quad. */
+	/* Clockwise winding and top/left initial vertex. */
 	{
 		.aligned   = true,
-		.box       = BOX (-0.50f, -0.50f,  0.50f,  0.50f),
-		.polygon   = QUAD(-0.25f, -0.25f,  0.25f,  0.25f),
-		.clipped   = QUAD(-0.25f, -0.25f,  0.25f,  0.25f),
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{-0.25f, -0.25f}, { 0.25f, -0.25f},
+			      { 0.25f,  0.25f}, {-0.25f,  0.25f}},
+		.clipped   = {{-0.25f, -0.25f}, { 0.25f, -0.25f},
+			      { 0.25f,  0.25f}, {-0.25f,  0.25f}},
 		.clipped_n = 4,
 	},
 
+	/* Clockwise winding and top/right initial vertex. */
+	{
+		.aligned   = true,
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{ 0.25f, -0.25f}, { 0.25f,  0.25f},
+			      {-0.25f,  0.25f}, {-0.25f, -0.25f}},
+		.clipped   = {{ 0.25f, -0.25f}, { 0.25f,  0.25f},
+			      {-0.25f,  0.25f}, {-0.25f, -0.25f}},
+		.clipped_n = 4,
+	},
+
+	/* Clockwise winding and bottom/right initial vertex. */
+	{
+		.aligned   = true,
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{ 0.25f,  0.25f}, {-0.25f,  0.25f},
+			      {-0.25f, -0.25f}, { 0.25f, -0.25f}},
+		.clipped   = {{ 0.25f,  0.25f}, {-0.25f,  0.25f},
+			      {-0.25f, -0.25f}, { 0.25f, -0.25f}},
+		.clipped_n = 4,
+	},
+
+	/* Clockwise winding and bottom/left initial vertex. */
+	{
+		.aligned   = true,
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{-0.25f,  0.25f}, {-0.25f, -0.25f},
+			      { 0.25f, -0.25f}, { 0.25f,  0.25f}},
+		.clipped   = {{-0.25f,  0.25f}, {-0.25f, -0.25f},
+			      { 0.25f, -0.25f}, { 0.25f,  0.25f}},
+		.clipped_n = 4,
+	},
+
+	/* Counter-clockwise winding and top/left initial vertex. */
+	{
+		.aligned   = true,
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{-0.25f, -0.25f}, {-0.25f,  0.25f},
+			      { 0.25f,  0.25f}, { 0.25f, -0.25f}},
+		.clipped   = {{-0.25f, -0.25f}, {-0.25f,  0.25f},
+			      { 0.25f,  0.25f}, { 0.25f, -0.25f}},
+		.clipped_n = 4,
+	},
+
+	/* Counter-clockwise winding and top/right initial vertex. */
+	{
+		.aligned   = true,
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{ 0.25f, -0.25f}, {-0.25f, -0.25f},
+			      {-0.25f,  0.25f}, { 0.25f,  0.25f}},
+		.clipped   = {{ 0.25f, -0.25f}, {-0.25f, -0.25f},
+			      {-0.25f,  0.25f}, { 0.25f,  0.25f}},
+		.clipped_n = 4,
+	},
+
+	/* Counter-clockwise winding and bottom/right initial vertex. */
+	{
+		.aligned   = true,
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{ 0.25f,  0.25f}, { 0.25f, -0.25f},
+			      {-0.25f, -0.25f}, {-0.25f,  0.25f}},
+		.clipped   = {{ 0.25f,  0.25f}, { 0.25f, -0.25f},
+			      {-0.25f, -0.25f}, {-0.25f,  0.25f}},
+		.clipped_n = 4,
+	},
+
+	/* Counter-clockwise winding and bottom/left initial vertex. */
+	{
+		.aligned   = true,
+		.box       = BOX(-0.50f, -0.50f,  0.50f,  0.50f),
+		.polygon   = {{-0.25f,  0.25f}, { 0.25f,  0.25f},
+			      { 0.25f, -0.25f}, {-0.25f, -0.25f}},
+		.clipped   = {{-0.25f,  0.25f}, { 0.25f,  0.25f},
+			      { 0.25f, -0.25f}, {-0.25f, -0.25f}},
+		.clipped_n = 4,
+	},
+
+	/* Miscellaneous cases: */
+
 	/* Box intersects entire same size aligned quad. */
 	{
 		.aligned   = true,