diff -r 133ee2b48e52 Lib/tarfile.py
--- a/Lib/tarfile.py	Fri Aug 01 23:51:51 2014 -0700
+++ b/Lib/tarfile.py	Sat Aug 02 08:52:20 2014 +0000
@@ -1297,7 +1297,7 @@
         # the longname information.
         next.offset = self.offset
         if self.type == GNUTYPE_LONGNAME:
-            next.name = nts(buf)
+            next.name = nts(buf).rstrip("/")
         elif self.type == GNUTYPE_LONGLINK:
             next.linkname = nts(buf)
 
diff -r 133ee2b48e52 Lib/test/test_tarfile.py
--- a/Lib/test/test_tarfile.py	Fri Aug 01 23:51:51 2014 -0700
+++ b/Lib/test/test_tarfile.py	Sat Aug 02 08:52:20 2014 +0000
@@ -759,6 +759,26 @@
                 "failed to store 100 char filename")
         tar.close()
 
+    def test_101_char_dir(self):
+        # Test for bug #21987.
+        name = "x" * 101
+        tar = tarfile.open(tmpname, self.mode)
+        cwd = os.getcwd()
+        try:
+            os.chdir(TEMPDIR)
+            os.mkdir(name)
+            tar.add(name)
+        finally:
+            os.rmdir(name)
+            os.chdir(cwd)
+            tar.close()
+
+        tar = tarfile.open(tmpname)
+        try:
+            tar.getmember(name)
+        finally:
+            tar.close()
+
     def test_tar_size(self):
         # Test for bug #1013882.
         tar = tarfile.open(tmpname, self.mode)