diff --git a/pkgs/development/tools/ocaml/findlib/default.nix b/pkgs/development/tools/ocaml/findlib/default.nix
index fb1eb4276d6..7d95963209a 100644
--- a/pkgs/development/tools/ocaml/findlib/default.nix
+++ b/pkgs/development/tools/ocaml/findlib/default.nix
@@ -32,7 +32,7 @@ stdenv.mkDerivation rec {
   setupHook = writeText "setupHook.sh" ''
     addOCamlPath () {
         if test -d "''$1/lib/ocaml/${ocaml.version}/site-lib"; then
-            export OCAMLPATH="''${OCAMLPATH}''${OCAMLPATH:+:}''$1/lib/ocaml/${ocaml.version}/site-lib/"
+            export OCAMLPATH="''${OCAMLPATH-}''${OCAMLPATH:+:}''$1/lib/ocaml/${ocaml.version}/site-lib/"
         fi
         if test -d "''$1/lib/ocaml/${ocaml.version}/site-lib/stublibs"; then
             export CAML_LD_LIBRARY_PATH="''${CAML_LD_LIBRARY_PATH}''${CAML_LD_LIBRARY_PATH:+:}''$1/lib/ocaml/${ocaml.version}/site-lib/stublibs"