diff --git a/dangerzone/args.py b/dangerzone/args.py
new file mode 100644
index 0000000..1665450
--- /dev/null
+++ b/dangerzone/args.py
@@ -0,0 +1,26 @@
+from typing import Optional
+
+import click
+
+from . import errors
+from .document import Document
+
+
+@errors.handle_document_errors
+def validate_input_filename(
+    ctx: click.Context, param: str, value: Optional[str]
+) -> Optional[str]:
+    if value is None:
+        return None
+    Document.validate_input_filename(value)
+    return value
+
+
+@errors.handle_document_errors
+def validate_output_filename(
+    ctx: click.Context, param: str, value: Optional[str]
+) -> Optional[str]:
+    if value is None:
+        return None
+    Document.validate_output_filename(value)
+    return value
diff --git a/dangerzone/cli.py b/dangerzone/cli.py
index 1c008b2..f51af9a 100644
--- a/dangerzone/cli.py
+++ b/dangerzone/cli.py
@@ -7,7 +7,7 @@ from typing import Optional
 import click
 from colorama import Back, Fore, Style
 
-from . import container, errors
+from . import args, container, errors
 from .container import convert
 from .document import Document
 from .global_common import GlobalCommon
@@ -20,9 +20,13 @@ def print_header(s: str) -> None:
 
 
 @click.command()
-@click.option("--output-filename", help="Default is filename ending with -safe.pdf")
+@click.option(
+    "--output-filename",
+    callback=args.validate_output_filename,
+    help="Default is filename ending with -safe.pdf",
+)
 @click.option("--ocr-lang", help="Language to OCR, defaults to none")
-@click.argument("filename", required=True)
+@click.argument("filename", required=True, callback=args.validate_input_filename)
 @errors.handle_document_errors
 def cli_main(
     output_filename: Optional[str], ocr_lang: Optional[str], filename: str
diff --git a/dangerzone/errors.py b/dangerzone/errors.py
index 5f6c84d..98b2759 100644
--- a/dangerzone/errors.py
+++ b/dangerzone/errors.py
@@ -1,9 +1,12 @@
 import functools
 import logging
 import sys
+from typing import Any, Callable, TypeVar, cast
 
 import click
 
+F = TypeVar("F", bound=Callable[..., Any])
+
 log = logging.getLogger(__name__)
 
 
@@ -11,11 +14,11 @@ class DocumentFilenameException(Exception):
     """Exception for document-related filename errors."""
 
 
-def handle_document_errors(func):
+def handle_document_errors(func: F) -> F:
     """Log document-related errors and exit gracefully."""
 
     @functools.wraps(func)
-    def wrapper(*args, **kwargs):
+    def wrapper(*args, **kwargs):  # type: ignore
         try:
             return func(*args, **kwargs)
         except DocumentFilenameException as e:
@@ -26,4 +29,4 @@ def handle_document_errors(func):
             click.echo(str(e))
             exit(1)
 
-    return wrapper
+    return cast(F, wrapper)
diff --git a/dangerzone/gui/__init__.py b/dangerzone/gui/__init__.py
index 5ca6fce..5aaafbb 100644
--- a/dangerzone/gui/__init__.py
+++ b/dangerzone/gui/__init__.py
@@ -10,7 +10,7 @@ import click
 import colorama
 from PySide2 import QtCore, QtGui, QtWidgets
 
-from .. import errors
+from .. import args, errors
 from ..document import Document
 from ..global_common import GlobalCommon
 from .common import GuiCommon
@@ -50,7 +50,7 @@ class ApplicationWrapper(QtCore.QObject):
 
 
 @click.command()
-@click.argument("filename", required=False)
+@click.argument("filename", required=False, callback=args.validate_input_filename)
 @errors.handle_document_errors
 def gui_main(filename: Optional[str]) -> bool:
     setup_logging()