diff --git a/libweston/vertex-clipping.c b/libweston/vertex-clipping.c
index 5aa26b4b..1ef840b9 100644
--- a/libweston/vertex-clipping.c
+++ b/libweston/vertex-clipping.c
@@ -295,8 +295,7 @@ clip_polygon_bottom(struct clip_context *ctx, const struct polygon8 *src,
  * https://www.codeguru.com/cplusplus/polygon-clipping/
  */
 WESTON_EXPORT_FOR_TESTS int
-clipper_clip(const struct clipper_vertex *polygon,
-	     size_t polygon_len,
+clipper_clip(const struct clipper_vertex polygon[4],
 	     const struct clipper_vertex box[2],
 	     struct clipper_vertex *restrict vertices)
 {
@@ -304,12 +303,9 @@ clipper_clip(const struct clipper_vertex *polygon,
 	struct polygon8 p, tmp;
 	int i, n;
 
-	if (polygon_len > 8)
-		return -1;
-
 	memcpy(ctx.box, box, 2 * sizeof *box);
-	memcpy(p.pos, polygon, polygon_len * sizeof *polygon);
-	p.n = polygon_len;
+	memcpy(p.pos, polygon, 4 * sizeof *polygon);
+	p.n = 4;
 	tmp.n = clip_polygon_left(&ctx, &p, tmp.pos);
 	p.n = clip_polygon_right(&ctx, &tmp, p.pos);
 	tmp.n = clip_polygon_top(&ctx, &p, tmp.pos);
@@ -390,7 +386,7 @@ clipper_quad_clip(struct clipper_quad *quad,
 
 	/* Then use our general purpose clipping algorithm:
 	 */
-	n = clipper_clip(quad->polygon, 4, box, vertices);
+	n = clipper_clip(quad->polygon, box, vertices);
 
 	if (n < 3)
 		return 0;
diff --git a/libweston/vertex-clipping.h b/libweston/vertex-clipping.h
index 5e63cf6f..1308fecc 100644
--- a/libweston/vertex-clipping.h
+++ b/libweston/vertex-clipping.h
@@ -42,15 +42,14 @@ struct clipper_quad {
 /*
  * General purpose clipping function. Compute the boundary vertices of the
  * intersection of a 'polygon' and a clipping 'box'. 'polygon' points to an
- * array of 'polygon_len' vertices, less than or equal to 8, defining a convex
- * polygon of any winding order. 'box' points to an array of 2 vertices where
- * the values of the 1st vertex are less than or equal to the values of the 2nd
- * vertex. Up to 16 resulting vertices, using 'polygon' winding order, are
- * written to 'vertices'. The return value is the number of vertices created.
+ * array of 4 vertices defining a convex polygon of any winding order. 'box'
+ * points to an array of 2 vertices where the values of the 1st vertex are less
+ * than or equal to the values of the 2nd vertex. Up to 8 resulting vertices,
+ * using 'polygon' winding order, are written to 'vertices'. The return value is
+ * the number of vertices created.
  */
 int
-clipper_clip(const struct clipper_vertex *polygon,
-	     size_t polygon_len,
+clipper_clip(const struct clipper_vertex polygon[4],
 	     const struct clipper_vertex box[2],
 	     struct clipper_vertex *restrict vertices);
 
diff --git a/tests/vertex-clip-test.c b/tests/vertex-clip-test.c
index 53f1883a..bea3be30 100644
--- a/tests/vertex-clip-test.c
+++ b/tests/vertex-clip-test.c
@@ -44,7 +44,6 @@ struct vertex_clip_test_data {
 	};
 	struct clipper_vertex polygon[8];
 	struct clipper_vertex clipped[8];
-	int polygon_n;
 	int clipped_n;
 	bool aligned;
 };
@@ -86,7 +85,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 		.box       = BOX (50.0f, 50.0f, 100.0f, 100.0f),
 		.polygon   = QUAD(51.0f, 51.0f,  99.0f,  99.0f),
 		.clipped   = QUAD(51.0f, 51.0f,  99.0f,  99.0f),
-		.polygon_n = 4,
 		.clipped_n = 4,
 	},
 
@@ -95,7 +93,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 		.box       = BOX (50.0f, 50.0f, 100.0f, 100.0f),
 		.polygon   = QUAD(51.0f, 51.0f,  99.0f, 101.0f),
 		.clipped   = QUAD(51.0f, 51.0f,  99.0f, 100.0f),
-		.polygon_n = 4,
 		.clipped_n = 4,
 	},
 
@@ -104,7 +101,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 		.box       = BOX (50.0f, 50.0f, 100.0f, 100.0f),
 		.polygon   = QUAD(51.0f, 49.0f,  99.0f,  99.0f),
 		.clipped   = QUAD(51.0f, 50.0f,  99.0f,  99.0f),
-		.polygon_n = 4,
 		.clipped_n = 4,
 	},
 
@@ -113,7 +109,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 		.box       = BOX (50.0f, 50.0f, 100.0f, 100.0f),
 		.polygon   = QUAD(49.0f, 51.0f,  99.0f,  99.0f),
 		.clipped   = QUAD(50.0f, 51.0f,  99.0f,  99.0f),
-		.polygon_n = 4,
 		.clipped_n = 4,
 	},
 
@@ -122,7 +117,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 		.box       = BOX (50.0f, 50.0f, 100.0f, 100.0f),
 		.polygon   = QUAD(51.0f, 51.0f, 101.0f,  99.0f),
 		.clipped   = QUAD(51.0f, 51.0f, 100.0f,  99.0f),
-		.polygon_n = 4,
 		.clipped_n = 4,
 	},
 
@@ -132,7 +126,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 		.polygon   = {{ 25.0f, 75.0f}, {75.0f,  25.0f},
 			      {125.0f, 75.0f}, {75.0f, 125.0f}},
 		.clipped   = QUAD(50.0f, 50.0f, 100.0f, 100.0f),
-		.polygon_n = 4,
 		.clipped_n = 4,
 	},
 
@@ -145,7 +138,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 			      {100.0f,  62.5f}, {100.0f,  87.5f},
 			      { 87.5f, 100.0f}, { 62.5f, 100.0f},
 			      { 50.0f,  87.5f}, { 50.0f,  62.5f}},
-		.polygon_n = 4,
 		.clipped_n = 8,
 	},
 
@@ -158,7 +150,6 @@ static const struct vertex_clip_test_data clip_expected_data[] = {
 			      { 50.0f,  87.5f}, { 62.5f, 100.0f},
 			      { 87.5f, 100.0f}, {100.0f,  87.5f},
 			      {100.0f,  62.5f}, { 87.5f,  50.0f}},
-		.polygon_n = 4,
 		.clipped_n = 8,
 	},
 };
@@ -169,19 +160,11 @@ TEST_P(clip_expected, clip_expected_data)
 	struct clipper_vertex clipped[8];
 	int clipped_n;
 
-	clipped_n = clipper_clip(tdata->polygon, tdata->polygon_n, tdata->box,
-				 clipped);
+	clipped_n = clipper_clip(tdata->polygon, tdata->box, clipped);
 
 	assert_vertices(clipped, clipped_n, tdata->clipped, tdata->clipped_n);
 }
 
-TEST(clip_size_too_high)
-{
-	struct clipper_vertex polygon[8] = {}, box[2] = {};
-
-	assert(clipper_clip(polygon, 9, box, NULL) == -1);
-}
-
 /* clipper_quad_clip() tests: */
 
 static const struct vertex_clip_test_data quad_clip_expected_data[] = {