diff --git a/nixos/modules/services/databases/postgresql.nix b/nixos/modules/services/databases/postgresql.nix
index 7963b4152fe6d3..530c4a036fad86 100644
--- a/nixos/modules/services/databases/postgresql.nix
+++ b/nixos/modules/services/databases/postgresql.nix
@@ -439,7 +439,7 @@ in
             ]);
             options = {
               shared_preload_libraries = mkOption {
-                type = nullOr (coercedTo (listOf str) (concatStringsSep ", ") str);
+                type = nullOr (coercedTo (listOf str) (concatStringsSep ",") commas);
                 default = null;
                 example = literalExpression ''[ "auto_explain" "anon" ]'';
                 description = ''