diff --git a/api/onnx_web/chain/upscale_outpaint.py b/api/onnx_web/chain/upscale_outpaint.py
index 253a881c8..602a7438f 100644
--- a/api/onnx_web/chain/upscale_outpaint.py
+++ b/api/onnx_web/chain/upscale_outpaint.py
@@ -11,7 +11,7 @@
 from ..output import save_image
 from ..params import Border, ImageParams, Size, SizeChart, StageParams
 from ..utils import ServerContext, is_debug
-from .utils import process_tile_spiral
+from .utils import process_tile_grid, process_tile_spiral
 
 logger = getLogger(__name__)
 
@@ -92,7 +92,16 @@ def outpaint(image: Image.Image, dims: Tuple[int, int, int]):
         draw_mask.rectangle((left, top, left + tile, top + tile), fill="black")
         return result.images[0]
 
-    output = process_tile_spiral(source_image, SizeChart.auto, 1, [outpaint])
+    margin_x = float(max(border.left, border.right))
+    margin_y = float(max(border.top, border.bottom))
+    overlap = min(margin_x / source_image.width, margin_y / source_image.height)
+
+    if overlap > 0 and border.left == border.right and border.top == border.bottom:
+        logger.debug("outpainting with an even border, using spiral tiling")
+        output = process_tile_spiral(source_image, SizeChart.auto, 1, [outpaint], overlap=overlap)
+    else:
+        logger.debug("outpainting with an uneven border, using grid tiling")
+        output = process_tile_grid(source_image, SizeChart.auto, 1, [outpaint])
 
     logger.info("final output image size: %sx%s", output.width, output.height)
     return output
diff --git a/api/onnx_web/chain/utils.py b/api/onnx_web/chain/utils.py
index 0e112303d..1bb3ac220 100644
--- a/api/onnx_web/chain/utils.py
+++ b/api/onnx_web/chain/utils.py
@@ -57,18 +57,17 @@ def process_tile_spiral(
     center_x = (width // 2) - (tile // 2)
     center_y = (height // 2) - (tile // 2)
 
-    # TODO: only valid for overlap = 0.5
-    if overlap == 0.5:
-        tiles = [
-            (0, tile * -overlap),
-            (tile * overlap, tile * -overlap),
-            (tile * overlap, 0),
-            (tile * overlap, tile * overlap),
-            (0, tile * overlap),
-            (tile * -overlap, tile * overlap),
-            (tile * -overlap, 0),
-            (tile * -overlap, tile * -overlap),
-        ]
+    # TODO: should add/remove tiles when overlap != 0.5
+    tiles = [
+        (0, tile * -overlap),
+        (tile * overlap, tile * -overlap),
+        (tile * overlap, 0),
+        (tile * overlap, tile * overlap),
+        (0, tile * overlap),
+        (tile * -overlap, tile * overlap),
+        (tile * -overlap, 0),
+        (tile * -overlap, tile * -overlap),
+    ]
 
     # tile tuples is source, multiply by scale for dest
     counter = 0