diff --git a/apsg/plotting.py b/apsg/plotting.py
index f6dad72..a121abc 100644
--- a/apsg/plotting.py
+++ b/apsg/plotting.py
@@ -222,16 +222,24 @@ def plane(self, obj, *args, **kwargs):
             x = []
             y = []
             for azi, inc in obj.dd.T:
-                xx, yy = self._cone(p2v(azi, inc), l2v(azi, inc),
-                                    limit=89.9999, res=cosd(inc) * 179 + 2)
+                xx, yy = self._cone(
+                    p2v(azi, inc),
+                    l2v(azi, inc),
+                    limit=89.9999,
+                    res=int(cosd(inc) * 179 + 2)
+                )
                 x = np.hstack((x, xx, np.nan))
                 y = np.hstack((y, yy, np.nan))
             x = x[:-1]
             y = y[:-1]
         else:
             azi, inc = obj.dd
-            x, y = self._cone(p2v(azi, inc), l2v(azi, inc),
-                              limit=89.9999, res=cosd(inc) * 179 + 2)
+            x, y = self._cone(
+                p2v(azi, inc),
+                l2v(azi, inc),
+                limit=89.9999,
+                res=int(cosd(inc) * 179 + 2)
+            )
         h = self.fig.axes[self.active].plot(x, y, *args, **kwargs)
         if animate:
             self.artists.append(tuple(h))