diff --git a/Lib/calendar.py b/Lib/calendar.py
index 92fe6b7723fe268..5eb04cbe7014676 100644
--- a/Lib/calendar.py
+++ b/Lib/calendar.py
@@ -609,11 +609,11 @@ def formatyearpage(self, theyear, width=3, css='calendar.css', encoding=None):
         content = self.formatyear(theyear, width)
         return self._format_html_page(theyear, content, css, encoding)
 
-    def formatmonthpage(self, theyear, themonth, width=3, css='calendar.css', encoding=None):
+    def formatmonthpage(self, theyear, themonth, css='calendar.css', encoding=None):
         """
         Return a formatted month as a complete HTML page.
         """
-        content = self.formatmonth(theyear, themonth, width)
+        content = self.formatmonth(theyear, themonth)
         return self._format_html_page(theyear, content, css, encoding)
 
 
diff --git a/Lib/test/test_calendar.py b/Lib/test/test_calendar.py
index 6ed27b4095bc1db..422ada039fc12c5 100644
--- a/Lib/test/test_calendar.py
+++ b/Lib/test/test_calendar.py
@@ -545,6 +545,12 @@ def test_format_html_year_with_month(self):
             result_2009_6_html
         )
 
+    def test_formatmonthpage_no_width(self):
+        # gh-140212: formatmonthpage must not accept a 'width' argument.
+        cal = calendar.HTMLCalendar()
+        self.assertIn(b'class="month">June 2009', cal.formatmonthpage(2009, 6))
+        self.assertRaises(TypeError, cal.formatmonthpage, 2009, 6, width=3)
+
 
 class CalendarTestCase(unittest.TestCase):
 
diff --git a/Misc/NEWS.d/next/Library/2026-07-06-10-30-00.gh-issue-153158.m0nthP.rst b/Misc/NEWS.d/next/Library/2026-07-06-10-30-00.gh-issue-153158.m0nthP.rst
new file mode 100644
index 000000000000000..3850860fb2f8db1
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-07-06-10-30-00.gh-issue-153158.m0nthP.rst
@@ -0,0 +1,3 @@
+Remove the erroneous *width* argument of
+:meth:`!calendar.HTMLCalendar.formatmonthpage`, which could drop the year from
+the heading.