diff --git a/README.md b/README.md
index 7eb9055..ffd2f3c 100644
--- a/README.md
+++ b/README.md
@@ -81,6 +81,19 @@ BELOW HERE BE DRAGONS
 %%                {ArchRegex, TargetFile, Sources}
 %%                {TargetFile, Sources}
 %%
+%%                Note that if you want to use any of the rebar3 variables
+%%                below you must MUST use a ${}-style to get the expansion
+%%                to work. e.g. to expand REBAR_DEPS_DIR, do something like:
+%%
+%%                {port_specs, [{"priv/nif.so",
+%%                               ["c_src/nif.c",
+%%                                "${REBAR_DEPS_DIR}/foo/bar.c"]}]}.
+%%
+%%                This is a _very_ good way to be able to use your code both
+%%                as a top level app and a dependency.
+%%
+%%                CAVEAT! Not using {} is broken for the moment.
+%%
 %% * port_env - Erlang list of key/value pairs which will control
 %%              the environment when running the compiler and linker.
 %%              Variables set in the surrounding system shell are taken
diff --git a/src/pc_compilation.erl b/src/pc_compilation.erl
index ed3f9e9..4c161b4 100644
--- a/src/pc_compilation.erl
+++ b/src/pc_compilation.erl
@@ -60,7 +60,7 @@ compile_and_link(State, Specs) ->
                   true ->
                       LinkLang = pc_port_specs:link_lang(Spec),
                       LinkTemplate = select_link_template(LinkLang, Target),
-                      Env = pc_port_specs:environment(Spec),
+                      Env = pc_port_specs:create_env(State, Spec),
                       Cmd = expand_command(LinkTemplate, Env,
                                            pc_util:strjoin(Bins, " "),
                                            Target),
@@ -97,7 +97,7 @@ compile_sources(Config, Specs) ->
           fun(Spec, Acc) ->
                   Sources = pc_port_specs:sources(Spec),
                   Type    = pc_port_specs:type(Spec),
-                  Env     = pc_port_specs:environment(Spec),
+                  Env     = pc_port_specs:create_env(Config, Spec),
                   compile_each(Config, Sources, Type, Env, Acc)
           end, {[], []}, Specs),
     %% Rewrite clang compile commands database file only if something
diff --git a/src/pc_port_specs.erl b/src/pc_port_specs.erl
index ab9de58..7f390be 100644
--- a/src/pc_port_specs.erl
+++ b/src/pc_port_specs.erl
@@ -30,8 +30,10 @@
 
 -export([
          construct/1,
+         create_env/2,
          %% spec accessors
          environment/1,
+         opts/1,
          objects/1,
          sources/1,
          target/1,
@@ -66,9 +68,14 @@ construct(State) ->
             {ok, [S || S <- Specs, S#spec.sources /= []]}
     end.
 
+create_env(State, Spec) ->
+    pc_port_specs:environment(Spec) ++
+        try_and_create_env(State).
+
 %% == Spec Accessors ==
 
 environment(#spec{opts = Opts})        -> proplists:get_value(env, Opts).
+opts(#spec{opts = Opts})               -> Opts.
 objects(#spec{objects = Objects})      -> Objects.
 sources(#spec{sources = Sources})      -> Sources.
 target(#spec{target = Target})         -> Target.
@@ -79,6 +86,13 @@ link_lang(#spec{link_lang = LinkLang}) -> LinkLang.
 %%% Internal Functions
 %%%===================================================================
 
+try_and_create_env(State) ->
+    _ = code:ensure_loaded(rebar_env),
+    case erlang:function_exported(rebar_env, create_env, 1) of
+        false -> [];
+        true -> rebar_env:create_env(State)
+    end.
+
 port_spec_from_legacy(Config) ->
     %% Get the target from the so_name variable
     Target = case rebar_state:get(Config, so_name, undefined) of
@@ -133,13 +147,15 @@ get_port_spec(Config, OsType, {Target, Sources}) ->
 get_port_spec(Config, OsType, {Arch, Target, Sources}) ->
     get_port_spec(Config, OsType, {Arch, Target, Sources, []});
 get_port_spec(Config, OsType, {_Arch, Target, Sources, Opts}) ->
+    Env = try_and_create_env(Config),
     SourceFiles =
         lists:flatmap(
           fun(Source) ->
-                  Source1 = rebar_utils:escape_chars(
-                              filename:join(rebar_state:dir(Config), Source)),
+                  Source1 = expand_env(Source, Env),
+                  Source2 = rebar_utils:escape_chars(
+                              filename:join(rebar_state:dir(Config), Source1)),
                   case filelib:wildcard(Source1) of
-                      [] -> [Source1];
+                      [] -> [Source2];
                       FileList -> FileList
                   end
           end, Sources),
@@ -162,6 +178,22 @@ get_port_spec(Config, OsType, {_Arch, Target, Sources, Opts}) ->
           objects   = ObjectFiles,
           opts      = [port_opt(Config, O) || O <- fill_in_defaults(Opts)]}.
 
+expand_env(Source, Env) ->
+    case rebar_string:chr(Source, $$) of
+        0 ->
+            %% No variables to expand. Also hides undef on older rebar3.
+            Source;
+        _ ->
+            lists:foldl(
+              fun({Key, Value}, Acc) ->
+                      %% TODO: the expand_env_variable/3 only expands
+                      %% variables delimited by whitespace and inside
+                      %% ${}. Either fix or add a new function to
+                      %% rebar3 or make a new function here in pc.
+                      rebar_utils:expand_env_variable(Acc, Key, Value)
+              end, Source, Env)
+    end.
+
 coerce_extension({win32, nt}, Target) ->
     switch_to_dll_or_exe(Target);
 coerce_extension(_OsType, Target) ->