diff --git a/fuzzers/017-clbprecyinit/top.py b/fuzzers/017-clbprecyinit/top.py
index 47718a6c..348ec7e4 100644
--- a/fuzzers/017-clbprecyinit/top.py
+++ b/fuzzers/017-clbprecyinit/top.py
@@ -3,21 +3,13 @@ random.seed(0)
 import os
 import re
 from prjxray import verilog
-
-
-def slice_xy():
-    '''Return (X1, X2), (Y1, Y2) from XRAY_ROI, exclusive end (for xrange)'''
-    # SLICE_X12Y100:SLICE_X27Y149
-    # Note XRAY_ROI_GRID_* is something else
-    m = re.match(
-        r'SLICE_X([0-9]*)Y([0-9]*):SLICE_X([0-9]*)Y([0-9]*)',
-        os.getenv('XRAY_ROI'))
-    ms = [int(m.group(i + 1)) for i in range(4)]
-    return ((ms[0], ms[2] + 1), (ms[1], ms[3] + 1))
-
+from prjxray import util
 
 CLBN = 400
-SLICEX, SLICEY = slice_xy()
+SLICEX, SLICEY = util.site_xy_minmax([
+    'SLICEL',
+    'SLICEM',
+])
 # 800
 SLICEN = (SLICEY[1] - SLICEY[0]) * (SLICEX[1] - SLICEX[0])
 print('//SLICEX: %s' % str(SLICEX))
diff --git a/prjxray/util.py b/prjxray/util.py
index facb89b3..5a5a8c3f 100644
--- a/prjxray/util.py
+++ b/prjxray/util.py
@@ -35,6 +35,27 @@ def get_roi():
     return Roi(db=db, x1=x1, x2=x2, y1=y1, y2=y2)
 
 
+def gen_sites_xy(site_types):
+    for _tile_name, site_name, _site_type in get_roi().gen_sites(site_types):
+        m = re.match(r'.*_X([0-9]*)Y([0-9]*)', site_name)
+        x, y = int(m.group(1)), int(m.group(2))
+        yield (site_name, (x, y))
+
+
+def site_xy_minmax(site_types):
+    '''Return (X1, X2), (Y1, Y2) from XY_ROI, exclusive end (for xrange)'''
+    xmin = 9999
+    xmax = -1
+    ymin = 9999
+    ymax = -1
+    for _site_name, (x, y) in gen_sites_xy(site_types):
+        xmin = min(xmin, x)
+        xmax = max(xmax, x)
+        ymin = min(ymin, y)
+        ymax = max(ymax, y)
+    return (xmin, xmax + 1), (ymin, ymax + 1)
+
+
 # we know that all bits for CLB MUXes are in frames 30 and 31, so filter all other bits
 def bitfilter_clb_mux(frame_idx, bit_idx):
     return frame_idx in [30, 31]