diff --git a/src/ocrmypdf/builtin_plugins/ghostscript.py b/src/ocrmypdf/builtin_plugins/ghostscript.py
index d1c6a628..c16e5714 100644
--- a/src/ocrmypdf/builtin_plugins/ghostscript.py
+++ b/src/ocrmypdf/builtin_plugins/ghostscript.py
@@ -18,13 +18,13 @@ log = logging.getLogger(__name__)
 
 @hookimpl
 def check_options(options):
-    gs_version = ghostscript.version()
     check_external_program(
         program='gs',
         package='ghostscript',
-        version_checker=gs_version,
+        version_checker=ghostscript.version,
         need_version='9.15',  # limited by Travis CI / Ubuntu 14.04 backports
     )
+    gs_version = ghostscript.version()
     if gs_version in ('9.24', '9.51'):
         raise MissingDependencyError(
             f"Ghostscript {gs_version} contains serious regressions and is not "
diff --git a/src/ocrmypdf/subprocess/__init__.py b/src/ocrmypdf/subprocess/__init__.py
index ed336d4b..f677af81 100644
--- a/src/ocrmypdf/subprocess/__init__.py
+++ b/src/ocrmypdf/subprocess/__init__.py
@@ -266,7 +266,7 @@ def check_external_program(
     *,
     program: str,
     package: str,
-    version_checker: Union[str, Callable],
+    version_checker: Callable,
     need_version: str,
     required_for: Optional[str] = None,
     recommended=False,
@@ -291,7 +291,7 @@ def check_external_program(
     try:
         if callable(version_checker):
             found_version = version_checker()
-        else:
+        else:  # deprecated
             found_version = version_checker
     except (CalledProcessError, FileNotFoundError, MissingDependencyError):
         _error_missing_program(program, package, required_for, recommended)