@@ -409,17 +409,19 @@ def get_yaxis_text2_transform(self, pad):
     def _invalidate_internal(self, *args, **kwargs):
         rmin, rmax = self.viewLim.intervaly
         rorigin = self.get_rorigin()
-        inner = self.spines['inner']
+        inner = self.spines.get('inner', None)
 
         if rorigin < rmin:
             width = (rmax - rmin) / (rmax - rorigin) * 0.5
             self.patch.set_width(width)
-            inner.set_visible(True)
-            inner.set_patch_circle((0.5, 0.5), 0.5 - width)
+            if inner:
+                inner.set_visible(True)
+                inner.set_patch_circle((0.5, 0.5), 0.5 - width)
         else:
             self.patch.set_width(0.5)
-            inner.set_patch_circle((0.5, 0.5), 0.0)
-            inner.set_visible(False)
+            if inner:
+                inner.set_patch_circle((0.5, 0.5), 0.0)
+                inner.set_visible(False)
 
         for line in self.lines:
             self._update_line_limits(line)