diff --git a/CHANGES b/CHANGES
index 08b7d5ca2..8fd107430 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,7 @@ Features:
 Bugfixes:
  - DS GX: Fix vertex texture transformation (fixes mgba.io/i/702)
  - DS GX: Automatically normalize winding culling calculations (fixes mgba.io/i/699)
+ - DS GX: Fixed viewport calculations (fixes mgba.io/i/709)
 Misc:
  - DS GX: Clean up and unify texture mapping
  - DS Core: Add symbol loading
diff --git a/src/ds/gx/software.c b/src/ds/gx/software.c
index ef62be465..61377aa26 100644
--- a/src/ds/gx/software.c
+++ b/src/ds/gx/software.c
@@ -498,7 +498,7 @@ static void _preparePoly(struct DSGXRenderer* renderer, struct DSGXVertex* verts
 	}
 
 	int32_t v0x = (v0->viewCoord[0] + v0w) * (int64_t) (v0->viewportWidth << 12) / (v0w * 2) + (v0->viewportX << 12);
-	int32_t v0y = (-v0->viewCoord[1] + v0w) * (int64_t) (v0->viewportHeight << 12) / (v0w * 2) + (v0->viewportY << 12);
+	int32_t v0y = (DS_VIDEO_VERTICAL_PIXELS << 12) - ((v0->viewCoord[1] + v0w) * (int64_t) (v0->viewportHeight << 12) / (v0w * 2) + (v0->viewportY << 12));
 	if (poly->minY > v0y >> 12) {
 		poly->minY = v0y >> 12;
 	}
@@ -515,7 +515,7 @@ static void _preparePoly(struct DSGXRenderer* renderer, struct DSGXVertex* verts
 			v1w = 1;
 		}
 		int32_t v1x = (v1->viewCoord[0] + v1w) * (int64_t) (v1->viewportWidth << 12) / (v1w * 2) + (v1->viewportX << 12);
-		int32_t v1y = (-v1->viewCoord[1] + v1w) * (int64_t) (v1->viewportHeight << 12) / (v1w * 2) + (v1->viewportY << 12);
+		int32_t v1y = (DS_VIDEO_VERTICAL_PIXELS << 12) - ((v1->viewCoord[1] + v1w) * (int64_t) (v1->viewportHeight << 12) / (v1w * 2) + (v1->viewportY << 12));
 		if (poly->minY > v1y >> 12) {
 			poly->minY = v1y >> 12;
 		}
@@ -574,7 +574,7 @@ static void _preparePoly(struct DSGXRenderer* renderer, struct DSGXVertex* verts
 		v1w = 1;
 	}
 	int32_t v1x = (v1->viewCoord[0] + v1w) * (int64_t) (v1->viewportWidth << 12) / (v1w * 2) + (v1->viewportX << 12);
-	int32_t v1y = (-v1->viewCoord[1] + v1w) * (int64_t) (v1->viewportHeight << 12) / (v1w * 2) + (v1->viewportY << 12);
+	int32_t v1y = (DS_VIDEO_VERTICAL_PIXELS << 12) - ((v1->viewCoord[1] + v1w) * (int64_t) (v1->viewportHeight << 12) / (v1w * 2) + (v1->viewportY << 12));
 
 	if (poly->minY > v1y >> 12) {
 		poly->minY = v1y >> 12;