diff --git a/pkgs/development/beam-modules/build-rebar3.nix b/pkgs/development/beam-modules/build-rebar3.nix
index ac40b76a78a..f783683cd4a 100644
--- a/pkgs/development/beam-modules/build-rebar3.nix
+++ b/pkgs/development/beam-modules/build-rebar3.nix
@@ -49,7 +49,7 @@ let
 
     postPatch = ''
       rm -f rebar rebar3
-    '';
+    '' + postPatch;
 
     configurePhase = if configurePhase == null
     then ''