diff --git a/src/rebar_otp_app.erl b/src/rebar_otp_app.erl
index 6b330cf..136c5cb 100644
--- a/src/rebar_otp_app.erl
+++ b/src/rebar_otp_app.erl
@@ -151,7 +151,7 @@ validate_modules(AppName, Mods) ->
             ok;
         MissingMods ->
             Msg2 = lists:flatten([io_lib:format("\t* ~p\n", [M]) || M <- MissingMods]),
-            ?ERROR("On or more .beam files exist that are not listed in ~p.app:\n~s",
+            ?ERROR("One or more .beam files exist that are not listed in ~p.app:\n~s",
                    [AppName, Msg2]),
             ?FAIL
     end.