diff --git a/src/rebar_app_utils.erl b/src/rebar_app_utils.erl
index 1fa870b..34d357a 100644
--- a/src/rebar_app_utils.erl
+++ b/src/rebar_app_utils.erl
@@ -89,7 +89,14 @@ app_applications(AppFile) ->
 app_vsn(AppFile) ->
     case load_app_file(AppFile) of
         {ok, _, AppInfo} ->
-            get_value(vsn, AppInfo, AppFile);
+            case get_value(vsn, AppInfo, AppFile) of
+                git ->
+                    Cmd = "git describe --tags --always",
+                    {ok, VsnString} = rebar_utils:sh(Cmd, []),
+                    string:strip(VsnString, right, $\n);
+                Version ->
+                    Version
+            end;
         {error, Reason} ->
             ?ABORT("Failed to extract vsn from ~s: ~p\n",
                    [AppFile, Reason])
diff --git a/src/rebar_otp_app.erl b/src/rebar_otp_app.erl
index 4f21a67..f92de5c 100644
--- a/src/rebar_otp_app.erl
+++ b/src/rebar_otp_app.erl
@@ -96,8 +96,13 @@ preprocess(Config, AppSrcFile) ->
             AppVars = load_app_vars(Config) ++ [{modules, ebin_modules()}],
             A1 = apply_app_vars(AppVars, AppData),
 
+
+            %% AppSrcFile may contain instructions for generating a vsn number
+            Vsn = rebar_app_utils:app_vsn(AppSrcFile),
+            A2 = lists:keystore(vsn, 1, A1, {vsn, Vsn}),
+
             %% Build the final spec as a string
-            Spec = io_lib:format("~p.\n", [{application, AppName, A1}]),
+            Spec = io_lib:format("~p.\n", [{application, AppName, A2}]),
 
             %% Setup file .app filename and write new contents
             AppFile = rebar_app_utils:app_src_to_app(AppSrcFile),