diff --git a/pkgs/development/ruby-modules/gem-config/default.nix b/pkgs/development/ruby-modules/gem-config/default.nix
index 6647d71bd006..a0d4b9adcbe3 100644
--- a/pkgs/development/ruby-modules/gem-config/default.nix
+++ b/pkgs/development/ruby-modules/gem-config/default.nix
@@ -183,7 +183,7 @@ in
 
   pg = attrs: {
     buildFlags = [
-      "--with-pg-config=${postgresql}/bin/pg_config"
+      "--with-pg-config=${postgresql.dev}/bin/pg_config"
     ];
   };