diff --git a/ppx/xlog_ppx.ml b/ppx/xlog_ppx.ml
index 0bf9e1e..907ad4f 100644
--- a/ppx/xlog_ppx.ml
+++ b/ppx/xlog_ppx.ml
@@ -2,32 +2,35 @@ open Ppxlib
 
 let log_expander ~ctxt (e : expression) (l : (arg_label * expression) list) : expression =
   let loc = Expansion_context.Extension.extension_point_loc ctxt in
-  let is_exn = begin match e.pexp_desc with
+  let open (val Ast_builder.make loc) in
+  let (is_exn, err) = begin match e.pexp_desc with
   | Pexp_ident { txt = Lident "trace"; _ }
   | Pexp_ident { txt = Lident "debug"; _ }
   | Pexp_ident { txt = Lident "info"; _ }
   | Pexp_ident { txt = Lident "warn"; _ }
-  | Pexp_ident { txt = Lident "error"; _ } -> false
-  | Pexp_ident { txt = Lident "exn"; _ } -> true
+  | Pexp_ident { txt = Lident "error"; _ } -> (false, None)
+  | Pexp_ident { txt = Lident "exn"; _ } -> (true, None)
   | _ ->
-      raise (Location.Error (Location.Error.make ~loc ~sub:[]
-                              "log type must be one of: trace, debug, info, warn, error, exn"))
-  end in
-  let open (val Ast_builder.make loc) in
-  if is_exn then
-    match l with
-    | [] ->
-      raise (Location.Error (Location.Error.make ~loc ~sub:[]
-                              "must provide exn value"))
-    | (_, v)::l ->
-        let application =
-          eapply (pexp_ident { txt = Lident "m"; loc}) (List.map snd l) in
-        [%expr [%e e] [%e v] (Printexc.get_raw_backtrace ()) ~__POS__ ~__FUNCTION__
-                      (fun m -> [%e application])]
-  else
-    let application =
-      eapply (pexp_ident { txt = Lident "m"; loc}) (List.map snd l) in
-    [%expr [%e e] ~__POS__ ~__FUNCTION__ (fun m -> [%e application])]
+      (false,
+       Some (pexp_extension @@ Location.error_extensionf ~loc
+             "log type must be one of: trace, debug, info, warn, error, exn"))
+  end in match err with
+  | Some err -> err
+  | None ->
+    if is_exn then
+      match l with
+      | [] ->
+        pexp_extension @@ Location.error_extensionf ~loc
+          "must provide exn value"
+      | (_, v)::l ->
+          let application =
+            eapply (pexp_ident { txt = Lident "m"; loc}) (List.map snd l) in
+          [%expr [%e e] [%e v] (Printexc.get_raw_backtrace ()) ~__POS__ ~__FUNCTION__
+                        (fun m -> [%e application])]
+    else
+      let application =
+        eapply (pexp_ident { txt = Lident "m"; loc}) (List.map snd l) in
+      [%expr [%e e] ~__POS__ ~__FUNCTION__ (fun m -> [%e application])]
 
 let log_extension =
   let pattern =