diff --git a/pkgs/development/compilers/openjdk/12.nix b/pkgs/development/compilers/openjdk/12.nix
index 29992fdae687..16c2fd766bce 100644
--- a/pkgs/development/compilers/openjdk/12.nix
+++ b/pkgs/development/compilers/openjdk/12.nix
@@ -114,7 +114,7 @@ let
       # Set JAVA_HOME automatically.
       mkdir -p $out/nix-support
       cat <<EOF > $out/nix-support/setup-hook
-      if [ -z "\$JAVA_HOME" ]; then export JAVA_HOME=$out/lib/openjdk; fi
+      if [ -z "\''${JAVA_HOME-}" ]; then export JAVA_HOME=$out/lib/openjdk; fi
       EOF
     '';