diff --git a/pdfplumber/cli.py b/pdfplumber/cli.py
index 91af3b2..f6fbd07 100644
--- a/pdfplumber/cli.py
+++ b/pdfplumber/cli.py
@@ -9,6 +9,10 @@ from typing import Any, DefaultDict, Dict, List
 from .pdf import PDF
 
 
+if len(sys.argv) == 1:
+    sys.argv.append('--help')
+
+
 def parse_page_spec(p_str: str) -> List[int]:
     if "-" in p_str:
         start, end = map(int, p_str.split("-"))