diff --git a/lib/matplotlib/axes/_subplots.py b/lib/matplotlib/axes/_subplots.py
index d2f7e4a4174e..4ff7b44dcd12 100644
--- a/lib/matplotlib/axes/_subplots.py
+++ b/lib/matplotlib/axes/_subplots.py
@@ -187,6 +187,18 @@ def _make_twin_axes(self, *kl, **kwargs):
         return ax2
 
 
+# this here to support cartopy which was using a private part of the
+# API to register their Axes subclasses.
+
+# In 3.1 this should be changed to a dict subclass that warns on use
+# In 3.3 to a dict subclass that raises a useful exception on use
+# In 3.4 should be removed
+
+# The slow timeline is to give cartopy enough time to get several
+# release out before we break them.
+_subplot_classes = {}
+
+
 @functools.lru_cache(None)
 def subplot_class_factory(axes_class=None):
     """
@@ -198,9 +210,16 @@ def subplot_class_factory(axes_class=None):
     """
     if axes_class is None:
         axes_class = Axes
-    return type("%sSubplot" % axes_class.__name__,
-                (SubplotBase, axes_class),
-                {'_axes_class': axes_class})
+    try:
+        # Avoid creating two different instances of GeoAxesSubplot...
+        # Only a temporary backcompat fix.  This should be removed in
+        # 3.4
+        return next(cls for cls in SubplotBase.__subclasses__()
+                    if cls.__bases__ == (SubplotBase, axes_class))
+    except StopIteration:
+        return type("%sSubplot" % axes_class.__name__,
+                    (SubplotBase, axes_class),
+                    {'_axes_class': axes_class})
 
 
 # This is provided for backward compatibility
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
index 6c1f7a2c4019..6afed91f34ff 100644
--- a/lib/matplotlib/tests/test_axes.py
+++ b/lib/matplotlib/tests/test_axes.py
@@ -5789,3 +5789,21 @@ def test_spines_properbbox_after_zoom():
                       None, False, False)
     bb2 = ax.spines['bottom'].get_window_extent(fig.canvas.get_renderer())
     np.testing.assert_allclose(bb.get_points(), bb2.get_points(), rtol=1e-6)
+
+
+def test_cartopy_backcompat():
+    import matplotlib
+    import matplotlib.axes
+    import matplotlib.axes._subplots
+
+    class Dummy(matplotlib.axes.Axes):
+        ...
+
+    class DummySubplot(matplotlib.axes.SubplotBase, Dummy):
+        _axes_class = Dummy
+
+    matplotlib.axes._subplots._subplot_classes[Dummy] = DummySubplot
+
+    FactoryDummySubplot = matplotlib.axes.subplot_class_factory(Dummy)
+
+    assert DummySubplot is FactoryDummySubplot