diff --git a/src/nix/copy.cc b/src/nix/copy.cc
index 66993ac21..23323a36e 100644
--- a/src/nix/copy.cc
+++ b/src/nix/copy.cc
@@ -40,6 +40,8 @@ struct CmdCopy : StorePathsCommand
             .shortName('s')
             .description("whether to try substitutes on the destination store (only supported by SSH)")
             .set(&substitute, Substitute);
+
+        realiseMode = Build;
     }
 
     std::string description() override