diff --git a/pkgs/applications/editors/emacs/elisp-packages/elpa-packages.nix b/pkgs/applications/editors/emacs/elisp-packages/elpa-packages.nix
index 2bfc2f18e97d..94ca0cdf0b6d 100644
--- a/pkgs/applications/editors/emacs/elisp-packages/elpa-packages.nix
+++ b/pkgs/applications/editors/emacs/elisp-packages/elpa-packages.nix
@@ -96,7 +96,7 @@ self: let
           ./build.sh -j$NIX_BUILD_CORES
         '';
 
-        postInstall = ''
+        postInstall = (old.postInstall or "") + "\n" + ''
           ./install.sh --prefix=$out
         '';
 
diff --git a/pkgs/applications/editors/emacs/elisp-packages/melpa-packages.nix b/pkgs/applications/editors/emacs/elisp-packages/melpa-packages.nix
index 39835c58b650..6190d25ce93d 100644
--- a/pkgs/applications/editors/emacs/elisp-packages/melpa-packages.nix
+++ b/pkgs/applications/editors/emacs/elisp-packages/melpa-packages.nix
@@ -186,7 +186,7 @@ let
             cd -
           '';
 
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             install -m=755 -D source/sqlite/emacsql-sqlite \
               $out/share/emacs/site-lisp/elpa/emacsql-sqlite-${old.version}/sqlite/emacsql-sqlite
           '';
@@ -301,7 +301,7 @@ let
             make
             popd
           '';
-          postInstall = ''
+          postInstall = (attrs.postInstall or "") + "\n" + ''
             outd=$(echo $out/share/emacs/site-lisp/elpa/libgit-**)
             mkdir $outd/build
             install -m444 -t $outd/build ./source/src/libegit2.so
@@ -426,7 +426,7 @@ let
             cd -
           '';
 
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             mkdir -p $out/bin
             install -m755 -Dt $out/bin ./source/server/telega-server
           '';
@@ -456,7 +456,7 @@ let
             pkgs.libtool
             (pkgs.zeromq.override { enableDrafts = true; })
           ];
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             mv $EZMQ_LIBDIR/emacs-zmq.* $out/share/emacs/site-lisp/elpa/zmq-*
             rm -r $out/share/emacs/site-lisp/elpa/zmq-*/src
             rm $out/share/emacs/site-lisp/elpa/zmq-*/Makefile
@@ -533,7 +533,7 @@ let
           ];
           # we need the proper out directory to exist, so we do this in the
           # postInstall instead of postBuild
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             pushd source/build >/dev/null
             make
             install -m444 -t $out/share/emacs/site-lisp/elpa/vterm-** ../*.so