diff --git a/pdoc/cli.py b/pdoc/cli.py
index d0dd7b9a..3fcd164a 100755
--- a/pdoc/cli.py
+++ b/pdoc/cli.py
@@ -432,7 +432,9 @@ def main(_args=None):
     global args
     args = _args or parser.parse_args()
 
-    warnings.simplefilter("once", DeprecationWarning)
+    # If warnings not externally managed, show deprecation warnings
+    if not sys.warnoptions:
+        warnings.simplefilter("once", DeprecationWarning)
 
     if args.close_stdin:
         sys.stdin.close()