diff --git a/examples/api/radar_chart.py b/examples/api/radar_chart.py
index 814f79425405..06b2fb1acb06 100644
--- a/examples/api/radar_chart.py
+++ b/examples/api/radar_chart.py
@@ -36,7 +36,7 @@ def radar_factory(num_vars, frame='circle'):
 
     """
     # calculate evenly-spaced axis angles
-    theta = np.linspace(0, 2*np.pi, num_vars, endpoint=False)
+    theta = np.linspace(0, 2 * np.pi, num_vars, endpoint=False)
 
     def draw_poly_patch(self):
         # rotate theta such that the first axis is at the top
@@ -60,18 +60,13 @@ class RadarAxes(PolarAxes):
         draw_patch = patch_dict[frame]
 
         def __init__(self, *args, **kwargs):
-            super().__init__(*args, **kwargs)
+            super(RadarAxes, self).__init__(*args, **kwargs)
             # rotate plot such that the first axis is at the top
             self.set_theta_zero_location('N')
 
-        def fill(self, *args, **kwargs):
-            """Override fill so that line is closed by default"""
-            closed = kwargs.pop('closed', True)
-            return super().fill(closed=closed, *args, **kwargs)
-
         def plot(self, *args, **kwargs):
             """Override plot so that line is closed by default"""
-            lines = super().plot(*args, **kwargs)
+            lines = super(RadarAxes, self).plot(*args, **kwargs)
             for line in lines:
                 self._close_line(line)
 
@@ -116,7 +111,7 @@ def unit_poly_verts(theta):
     This polygon is circumscribed by a unit circle centered at (0.5, 0.5)
     """
     x0, y0, r = [0.5] * 3
-    verts = [(r*np.cos(t) + x0, r*np.sin(t) + y0) for t in theta]
+    verts = [(r * np.cos(t) + x0, r * np.sin(t) + y0) for t in theta]
     return verts
 
 
diff --git a/lib/matplotlib/projections/polar.py b/lib/matplotlib/projections/polar.py
index 1493d7b3fc02..047941628eb0 100644
--- a/lib/matplotlib/projections/polar.py
+++ b/lib/matplotlib/projections/polar.py
@@ -858,6 +858,34 @@ def __init__(self, *args, **kwargs):
         self.cla()
     __init__.__doc__ = Axes.__init__.__doc__
 
+    def add_patch(self, patch):
+        """
+        Override the existing add_patch() method from _AxesBase class.
+        The _interpolation_steps field should be revised prior to drawing.
+
+        :param patch: `~matplotlib.patches.Patch`
+        :return: `~matplotlib.patches.Patch`
+        """
+        patch.get_path()._interpolation_steps = \
+            max(patch.get_path()._interpolation_steps,  # default 1
+                maxis.GRIDLINE_INTERPOLATION_STEPS)  # 180
+        return super().add_patch(patch)
+
+    def fill(self, *args, **kwargs):
+        '''
+        Override the existing fill() method from _AxesBase class.
+        Filling a polygon to a polar axis, the edge of the polygon should
+        produce a straight line in polar space, thus the edges should not be
+        interpolated.
+
+        :return: list of `~matplotlib.patches.Patch`
+        '''
+        patches = super().fill(*args, **kwargs)
+        for polygon in patches:
+            polygon.get_path()._interpolation_steps = \
+                min(polygon.get_path()._interpolation_steps, 1)
+        return patches
+
     def cla(self):
         Axes.cla(self)
 
diff --git a/lib/matplotlib/tests/baseline_images/test_patches/polar_polygon_filling.png b/lib/matplotlib/tests/baseline_images/test_patches/polar_polygon_filling.png
new file mode 100644
index 000000000000..1d2f3216478d
Binary files /dev/null and b/lib/matplotlib/tests/baseline_images/test_patches/polar_polygon_filling.png differ
diff --git a/lib/matplotlib/tests/baseline_images/test_patches/transform_rectangle.png b/lib/matplotlib/tests/baseline_images/test_patches/transform_rectangle.png
new file mode 100644
index 000000000000..167e8f046c61
Binary files /dev/null and b/lib/matplotlib/tests/baseline_images/test_patches/transform_rectangle.png differ
diff --git a/lib/matplotlib/tests/test_patches.py b/lib/matplotlib/tests/test_patches.py
index ff1abb9c64f4..f82ae3602c13 100644
--- a/lib/matplotlib/tests/test_patches.py
+++ b/lib/matplotlib/tests/test_patches.py
@@ -363,6 +363,29 @@ def test_connection_patch():
     ax2.add_artist(con)
 
 
+@image_comparison(baseline_images=['transform_rectangle'], extensions=['png'],
+                  style='mpl20', remove_text=True)
+def test_polar_rectangle_transform_patch():
+    # Rectangle patch not transformed correctly in polar plot (#8521)
+    rectangle = mpatches.Rectangle((0, 1), width=np.pi * 0.5, height=1)
+    fig = plt.figure(figsize=(6, 8))
+    ax = fig.add_subplot(1, 1, 1, polar=True)
+    ax.add_patch(rectangle)
+    ax.set_rmax(2.5)
+
+
+@image_comparison(baseline_images=['polar_polygon_filling'],
+                  extensions=['png'], style='mpl20', remove_text=True)
+def test_polar_polygon_filling():
+    x = np.linspace(0, np.pi, 5)
+    y = np.abs(np.sin(x))
+    fig = plt.figure(figsize=(6.4, 4.8))
+    ax = fig.add_subplot(1, 1, 1, polar=True)
+    # ax.set_rmax(1.5)
+    ax.plot(x, y)
+    ax.fill(x, y)
+
+
 def test_datetime_rectangle():
     # Check that creating a rectangle with timedeltas doesn't fail
     from datetime import datetime, timedelta