diff --git a/numpy/testing/_private/utils.py b/numpy/testing/_private/utils.py
index 0e2f8ba9111e..a3832fcdef52 100644
--- a/numpy/testing/_private/utils.py
+++ b/numpy/testing/_private/utils.py
@@ -687,6 +687,8 @@ def assert_array_compare(comparison, x, y, err_msg='', verbose=True,
                          equal_inf=True):
     __tracebackhide__ = True  # Hide traceback for py.test
     from numpy.core import array, isnan, inf, bool_
+    from numpy.core.fromnumeric import all as npall
+
     x = array(x, copy=False, subok=True)
     y = array(y, copy=False, subok=True)
 
@@ -697,14 +699,21 @@ def istime(x):
         return x.dtype.char in "Mm"
 
     def func_assert_same_pos(x, y, func=isnan, hasval='nan'):
-        """Handling nan/inf: combine results of running func on x and y,
-        checking that they are True at the same locations."""
-        # Both the != True comparison here and the cast to bool_ at
-        # the end are done to deal with `masked`, which cannot be
-        # compared usefully, and for which .all() yields masked.
+        """Handling nan/inf.
+
+        Combine results of running func on x and y, checking that they are True
+        at the same locations.
+
+        """
+        # Both the != True comparison here and the cast to bool_ at the end are
+        # done to deal with `masked`, which cannot be compared usefully, and
+        # for which np.all yields masked.  The use of the function np.all is
+        # for back compatibility with ndarray subclasses that changed the
+        # return values of the all method.  We are not committed to supporting
+        # such subclasses, but some used to work.
         x_id = func(x)
         y_id = func(y)
-        if (x_id == y_id).all() != True:
+        if npall(x_id == y_id) != True:
             msg = build_err_msg([x, y],
                                 err_msg + '\nx and y %s location mismatch:'
                                 % (hasval), verbose=verbose, header=header,