diff --git a/gridcorner.py b/gridcorner.py
index bbd56ad238f45df837b4643f4ed73d6976ad2189..304f0a2179f1cdd8460d43635b14a090d23451ef 100644
--- a/gridcorner.py
+++ b/gridcorner.py
@@ -160,7 +160,7 @@ def gridcorner(D, xyz, labels=None, projection='max_slice', max_n_ticks=4,
 
 
 def projection_2D(ax, x, y, D, xidx, yidx, projection, lines=None, **kwargs):
-    flat_idxs = range(D.ndim)
+    flat_idxs = list(range(D.ndim))
     flat_idxs.remove(xidx)
     flat_idxs.remove(yidx)
     D2D = projection(D, axis=tuple(flat_idxs), **kwargs)
@@ -174,7 +174,7 @@ def projection_2D(ax, x, y, D, xidx, yidx, projection, lines=None, **kwargs):
 
 def projection_1D(ax, x, D, xidx, projection, showDvals=True, lines=None,
                   **kwargs):
-    flat_idxs = range(D.ndim)
+    flat_idxs = list(range(D.ndim))
     flat_idxs.remove(xidx)
     D1D = projection(D, axis=tuple(flat_idxs), **kwargs)
     ax.plot(x, D1D, color='k')