diff --git a/fuzzers/074-dump_all/generate_after_dump.sh b/fuzzers/074-dump_all/generate_after_dump.sh
index 064a38c6..9b432dfd 100755
--- a/fuzzers/074-dump_all/generate_after_dump.sh
+++ b/fuzzers/074-dump_all/generate_after_dump.sh
@@ -18,5 +18,6 @@ if [ -f $BASE_TILEGRID ]; then
   mv output/tilegrid.json output/tilegrid_full.json.tmp
   python3 ../../utils/merge_tilegrid.py \
     --base_grid $BASE_TILEGRID \
-    --overlay_grid output/tilegrid_full.json.tm \
-    --output_grid output/tilegrid.json
+    --overlay_grid output/tilegrid_full.json.tmp \
+    --output_grid output/tilegrid.json \
+    --mark_roi
diff --git a/minitests/roi_harness/Makefile b/minitests/roi_harness/Makefile
index 2a1759d4..77581545 100644
--- a/minitests/roi_harness/Makefile
+++ b/minitests/roi_harness/Makefile
@@ -2,7 +2,7 @@ BUILD_DIR=build
 
 # official demo configuration
 all:
-	SMALL=Y BUILD_DIR=$(BUILD_DIR) XRAY_PINCFG=BASYS3-SWBUT ./runme.sh
+	BUILD_DIR=$(BUILD_DIR) XRAY_PINCFG=BASYS3-SWBUT ./runme.sh
 
 clean:
 	rm -rf specimen_[0-9][0-9][0-9]/ seg_clblx.segbits vivado*.log vivado_*.str vivado*.jou design *.bits *.dcp *.bit design.txt .Xil
diff --git a/prjxray/connections.py b/prjxray/connections.py
index 14416fce..334d2f4e 100644
--- a/prjxray/connections.py
+++ b/prjxray/connections.py
@@ -6,7 +6,7 @@ Connection = namedtuple('Connection', 'wire_a wire_b')
 
 class Connections(object):
     def __init__(self, tilegrid, tileconn, tile_wires):
-        self.grid = tilegrid['tiles']
+        self.grid = tilegrid
         self.tile_wires = tile_wires
         self.coord_to_tile = {}
         self.coord_to_tile_type = {}
diff --git a/prjxray/grid.py b/prjxray/grid.py
index 8f1a6ed2..df1a6a1b 100644
--- a/prjxray/grid.py
+++ b/prjxray/grid.py
@@ -1,7 +1,7 @@
 from collections import namedtuple
 
 GridLoc = namedtuple('GridLoc', 'grid_x grid_y')
-GridInfo = namedtuple('GridInfo', 'segment sites tile_type')
+GridInfo = namedtuple('GridInfo', 'segment sites tile_type in_roi')
 
 
 class Grid(object):
@@ -16,15 +16,23 @@ class Grid(object):
         self.loc = {}
         self.tileinfo = {}
 
-        for tile in self.tilegrid['tiles']:
-            tileinfo = self.tilegrid['tiles'][tile]
+        for tile in self.tilegrid:
+            tileinfo = self.tilegrid[tile]
             grid_loc = GridLoc(tileinfo['grid_x'], tileinfo['grid_y'])
             assert grid_loc not in self.loc
             self.loc[grid_loc] = tile
+
+            if 'in_roi' in tileinfo:
+                in_roi = tileinfo['in_roi']
+            else:
+                in_roi = True
+
             self.tileinfo[tile] = GridInfo(
                 segment=tileinfo['segment'] if 'segment' in tileinfo else None,
                 sites=tileinfo['sites'],
-                tile_type=tileinfo['type'])
+                tile_type=tileinfo['type'],
+                in_roi=in_roi,
+            )
 
         x, y = zip(*self.loc.keys())
         self._dims = (min(x), max(x), min(y), max(y))
@@ -45,7 +53,7 @@ class Grid(object):
         return grid_loc in self.loc
 
     def loc_of_tilename(self, tilename):
-        tileinfo = self.tilegrid['tiles'][tilename]
+        tileinfo = self.tilegrid[tilename]
         return GridLoc(tileinfo['grid_x'], tileinfo['grid_y'])
 
     def tilename_at_loc(self, grid_loc):
diff --git a/utils/merge_tilegrid.py b/utils/merge_tilegrid.py
index b9b171cb..eeb376fc 100644
--- a/utils/merge_tilegrid.py
+++ b/utils/merge_tilegrid.py
@@ -9,12 +9,17 @@ def main():
     parser.add_argument('--output_grid', required=True)
     parser.add_argument('--overlay_grid', required=True)
     parser.add_argument('--old_format', action='store_true')
+    parser.add_argument('--mark_roi', action='store_true')
 
     args = parser.parse_args()
 
     with open(args.base_grid) as f:
         base_grid = json.load(f)
 
+    if args.mark_roi:
+        for tile in base_grid:
+            base_grid[tile]['in_roi'] = True
+
     with open(args.overlay_grid) as f:
         overlay_grid = json.load(f)
 
@@ -31,6 +36,8 @@ def main():
                     base_grid[tile][k] = overlay_grid[tile][k]
         else:
             base_grid[tile] = overlay_grid[tile]
+            if args.mark_roi:
+                base_grid[tile]['in_roi'] = False
 
     with open(args.output_grid, 'w') as f:
         json.dump(base_grid, f, indent=2)