diff --git a/dedalus/core/basis.py b/dedalus/core/basis.py
index 68ba5a6e..c67567c1 100644
--- a/dedalus/core/basis.py
+++ b/dedalus/core/basis.py
@@ -3600,7 +3600,7 @@ def forward_regularity_recombination(self, tensorsig, axis, gdata, ell_maps):
             Q = self.radial_recombinations(tensorsig, ell_list)
             # Flatten tensor axes
             shape = gdata.shape
-            temp = gdata.reshape((-1,)+shape[rank:])
+            temp = gdata.reshape((np.prod(shape[:rank]),)+shape[rank:])
             slices = [slice(None) for i in range(temp.ndim)]
             # Apply Q transformations for each ell to flattened tensor data
             for ell, m_ind, ell_ind in ell_maps:
@@ -3617,7 +3617,7 @@ def backward_regularity_recombination(self, tensorsig, axis, gdata, ell_maps):
             Q = self.radial_recombinations(tensorsig, ell_list)
             # Flatten tensor axes
             shape = gdata.shape
-            temp = gdata.reshape((-1,)+shape[rank:])
+            temp = gdata.reshape((np.prod(shape[:rank]),)+shape[rank:])
             slices = [slice(None) for i in range(temp.ndim)]
             # Apply Q transformations for each ell to flattened tensor data
             for ell, m_ind, ell_ind in ell_maps: