Shopify  (SHOP - Get Report) said late Monday it is acquiring 6 River Systems for $450 million in cash and stock.

The deal will gain Shopify additional capacity for fulfillment. The company said it will improve delivery times and cut costs.

Shopify said the deal consisting of approximately 60% in cash and 40% in Shopify Class A Subordinate Voting Shares, is expected to close in the fourth quarter.

Shopify shares fell $21.75, or 5.7% to $358.67 in regular trading ahead of the announcement. Shares were little changed in after hours action.