diff --git a/Lib/inspect.py b/Lib/inspect.py
index fdb5e2a..bb31098 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -1127,7 +1127,7 @@
     elif missing == 2:
         s = "{} and {}".format(*names)
     else:
-        tail = ", {} and {}".format(names[-2:])
+        tail = ", {} and {}".format(*names[-2:])
         del names[-2:]
         s = ", ".join(names) + tail
     raise TypeError("%s() missing %i required %s argument%s: %s" %
diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index b943530..881ca95 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -1216,6 +1216,12 @@
             inspect.getcallargs(f5)
 
 
+        # issue20817:
+        def f6(a, b, c):
+            pass
+        with self.assertRaisesRegex(TypeError, "'a', 'b' and 'c'"):
+            inspect.getcallargs(f6)
+
 class TestGetcallargsMethods(TestGetcallargsFunctions):
 
     def setUp(self):
diff --git a/Misc/NEWS b/Misc/NEWS
index fa774ba..3d62992 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -116,6 +116,9 @@
 - Issue #20816: Fix inspect.getcallargs() to raise correct TypeError for
   missing keyword-only arguments. Patch by Jeremiah Lowin.
 
+- Issue #20817: Fix inspect.getcallargs() to fail correctly if more
+  than 3 arguments are missing. Patch by Jeremiah Lowin.
+
 Documentation
 -------------