diff --git a/Lib/test/test_buffer.py b/Lib/test/test_buffer.py
@@ -2730,6 +2730,10 @@ def test_memoryview_cast_1D_ND(self):
         # be 1D, at least one format must be 'c', 'b' or 'B'.
         for _tshape in gencastshapes():
             for char in fmtdict['@']:
+                # Casts to _Bool are undefined if the source contains values
+                # other than 0 or 1.
+                if char == "?":
+                    continue
                 tfmt = ('', '@')[randrange(2)] + char
                 tsize = struct.calcsize(tfmt)
                 n = prod(_tshape) * tsize