diff --git a/AMULET.py b/AMULET.py
index 35b25ee..1f682ba 100644
--- a/AMULET.py
+++ b/AMULET.py
@@ -44,7 +44,11 @@ def generateMatrix(data, cellids, unionoverlaps):
 
     regioninfo = dict()
     
-    matrix = np.zeros((len(unionoverlaps), len(cellids)))
+    # Indicator matrix only ever stores 0/1 (peak-in-cell), so int8 is
+    # sufficient and 8x smaller than the float64 default.  This is the
+    # binding memory constraint for high-per-cell-coverage assays
+    # (e.g. 10x Chromium multiome at 25K+ cells/library).  See #28.
+    matrix = np.zeros((len(unionoverlaps), len(cellids)), dtype=np.int8)
     for i in range(len(data)):
         curchr = data[i,0]
         curstart = data[i,1]