diff --git a/lib/matplotlib/transforms.py b/lib/matplotlib/transforms.py
index 112b867abb22..51182616b8a0 100644
--- a/lib/matplotlib/transforms.py
+++ b/lib/matplotlib/transforms.py
@@ -1227,14 +1227,16 @@ class Transform(TransformNode):
 
     def __init_subclass__(cls):
         # 1d transforms are always separable; we assume higher-dimensional ones
-        # are not but subclasses can also directly set is_separable.
-        if ("is_separable" not in vars(cls)  # Was it overridden explicitly?
+        # are not but subclasses can also directly set is_separable -- this is
+        # verified by checking whether "is_separable" appears more than once in
+        # the class's MRO (it appears once in Transform).
+        if (sum("is_separable" in vars(parent) for parent in cls.__mro__) == 1
                 and cls.input_dims == cls.output_dims == 1):
             cls.is_separable = True
         # Transform.inverted raises NotImplementedError; we assume that if this
         # is overridden then the transform is invertible but subclass can also
         # directly set has_inverse.
-        if ("has_inverse" not in vars(cls)  # Was it overridden explicitly?
+        if (sum("has_inverse" in vars(parent) for parent in cls.__mro__) == 1
                 and hasattr(cls, "inverted")
                 and cls.inverted is not Transform.inverted):
             cls.has_inverse = True