diff --git a/src/state/opamEnv.ml b/src/state/opamEnv.ml
index ea156a25aa4..bf722975f36 100644
--- a/src/state/opamEnv.ml
+++ b/src/state/opamEnv.ml
@@ -247,6 +247,13 @@ let get_opam_raw ?(set_opamroot=false) ?(set_opamswitch=false) ~force_path
     root switch =
   let env_file = OpamPath.Switch.environment root switch in
   let upd = OpamFile.Environment.safe_read env_file in
+  let upd =
+    ("OPAM_SWITCH_PREFIX", Eq,
+     OpamFilename.Dir.to_string (OpamPath.Switch.root root switch),
+     Some "Prefix of the current opam switch") ::
+    List.filter (function ("OPAM_SWITCH_PREFIX", Eq, _, _) -> false | _ -> true)
+      upd
+  in
   let upd =
     if force_path then
       List.map (function