diff --git a/include/jobs.hrl b/include/jobs.hrl
index 7cf45e4..47ec97e 100644
--- a/include/jobs.hrl
+++ b/include/jobs.hrl
@@ -102,7 +102,7 @@
 -record(queue, {name                 :: any(),
 		mod                  :: atom(),
 		type = fifo          :: fifo | #producer{} | #passive{}
-				      | #action{},
+                                      | #action{},
 		group                :: atom(),
 		regulators  = []     :: [regulator() | regulator_ref()],
 		max_time             :: undefined | integer(),
@@ -114,7 +114,7 @@
 		check_counter = 0    :: integer(),
 		waiters = []         :: [{pid(), reference()}],
 		st
-	       }).
+               }).
 
 -record(sampler, {name,
                   mod,
diff --git a/rebar.config b/rebar.config
index 5fe82b5..85fe2ab 100644
--- a/rebar.config
+++ b/rebar.config
@@ -1,7 +1,11 @@
 %% -*- erlang -*-
+{erl_first_files,
+ ["src/jobs_queue.erl", "src/jobs_sampler.erl"]}.
 {erl_opts, [debug_info]}.
 {xref_checks, [undefined_function_calls]}.
 
+{require_otp_vsn, "R15|R16"}.
+
 {cover_enabled, true}.
 {eunit_opts, [verbose]}.
 
diff --git a/src/jobs_queue.erl b/src/jobs_queue.erl
index e0b4ad2..dfcc387 100644
--- a/src/jobs_queue.erl
+++ b/src/jobs_queue.erl
@@ -36,35 +36,33 @@
          delete/1]).
 -export([in/3,
          out/2,
-	 peek/1,
+         peek/1,
          info/2,
          all/1,
          empty/1,
          is_empty/1,
          timedout/1, timedout/2]).
 
--export([behaviour_info/1]).
-
 -include("jobs.hrl").
--import(jobs_lib, [timestamp/0]).
 
 -record(st, {table}).
 
 %-type timestamp() :: integer().
 -type job()       :: {pid(), reference()}.
 -type entry()     :: {timestamp(), job()}.
+-type info_item() :: max_time | oldest_job | length.
 
-behaviour_info(callbacks) ->
-    [{new    , 2},
-     {delete , 1},
-     {in     , 3},
-     {peek   , 1},
-     {out    , 2},
-     {all    , 1},
-     {info   , 2}];
-behaviour_info(_) ->
-    undefined.
+-callback new(fifo | lifo, #queue{}) -> #queue{}.
+-callback delete(#queue{}) -> any().
+-callback in(timestamp(), job(), #queue{}) -> #queue{}.
+-callback peek(#queue{}) -> entry().
+-callback out(N :: integer(), #queue{}) -> {[entry()], #queue{}}.
+-callback all(#queue{}) -> [entry()].
+-callback info(info_item(), #queue{}) -> any().
 
+-export_type([job/0,
+              entry/0,
+              info_item/0]).
 
 %% @spec new(Options, #queue{}) -> #queue{}
 %% @doc Instantiate a new queue.
@@ -146,9 +144,6 @@ out(N,#queue{st = #st{table = T}}=Q) when N >= 0 ->
 all(#queue{st = #st{table = T}}) ->
     ets:select(T, [{{'$1'},[],['$1']}]).
 
-
--type info_item() :: max_time | oldest_job | length.
-
 -spec info(info_item(), #queue{}) -> any().
 %% @spec info(Item, #queue{}) -> Info
 %%   Item = max_time | oldest_job | length
@@ -172,7 +167,7 @@ timedout(#queue{max_time = TO} = Q) ->
 
 timedout(_ , #queue{oldest_job = undefined}) -> [];
 timedout(TO, #queue{st = #st{table = Tab}} = Q) ->
-    Now = timestamp(),
+    Now = jobs_lib:timestamp(),
     {Objs, OJ} = find_expired(Tab, Now, TO),
     {Objs, Q#queue{oldest_job = OJ}}.
 
diff --git a/src/jobs_queue_list.erl b/src/jobs_queue_list.erl
index 6d3fc63..6ab768d 100644
--- a/src/jobs_queue_list.erl
+++ b/src/jobs_queue_list.erl
@@ -27,10 +27,13 @@
 -author('ulf.wiger@erlang-solutions.com').
 -copyright('Erlang Solutions Ltd.').
 
+-behaviour(jobs_queue).
+
 -export([new/2,
          delete/1]).
 -export([in/3,
          out/2,
+         peek/1,
          info/2,
          all/1,
          empty/1,
@@ -73,6 +76,12 @@ out(N, #queue{st = L, oldest_job = OJ} = Q) when N >= 0 ->
 	  end,
     {Out, Q#queue{st = Rest, oldest_job = OJ1}}.
 
+peek(#queue { st = []}) ->
+    undefined;
+peek(#queue { st = [H|_]}) ->
+    H.
+
+
 split(N, L) ->
     split(N, L, []).
 
diff --git a/src/jobs_sampler.erl b/src/jobs_sampler.erl
index ace59f1..8b8dda8 100644
--- a/src/jobs_sampler.erl
+++ b/src/jobs_sampler.erl
@@ -25,19 +25,18 @@
 -module(jobs_sampler).
 
 -export([start_link/0, start_link/1,
-	 trigger_sample/0,
-	 tell_sampler/2,
-	 subscribe/0,
-	 end_subscription/0,
-	 calc/3]).
+         trigger_sample/0,
+         tell_sampler/2,
+         subscribe/0,
+         end_subscription/0,
+         calc/3]).
 
 -export([init/1,
-	 behaviour_info/1,
-	 handle_call/3,
-	 handle_cast/2,
-	 handle_info/2,
-	 terminate/2,
-	 code_change/3]).
+         handle_call/3,
+         handle_cast/2,
+         handle_info/2,
+         terminate/2,
+         code_change/3]).
 
 -include("jobs.hrl").
 
@@ -59,13 +58,14 @@
                 modifiers = orddict:new(),
 		remote_modifiers = []}).
 
-
-behaviour_info(callbacks) ->
-    [{init, 2},
-     {sample, 2},
-     {handle_msg, 3},
-     {calc, 2}].
-
+-callback init(atom(), proplists:proplist()) ->
+    {ok, State :: term()}.
+-callback sample(timestamp(), State :: term()) ->
+    {Res :: term(), NState :: term()} | ignore.
+-callback handle_msg(M :: term(), TS :: timestamp(), State :: term()) ->
+    {ignore, NState :: term()} | {log, L :: term(), NState :: term()}.
+-callback calc(History :: term(), State :: term()) ->
+    {[{Q :: atom(), Val :: integer()}], NState :: term()}.
 
 trigger_sample() ->
     gen_server:cast(?MODULE, sample).