diff --git a/src/testdir/test_textformat.vim b/src/testdir/test_textformat.vim
index 6402989..3850213 100644
--- a/src/testdir/test_textformat.vim
+++ b/src/testdir/test_textformat.vim
@@ -238,7 +238,33 @@
   END
   call assert_equal(expected, getline(1, '$'))
 
-  " Using "o" repeats the line comment, "O" does not.
+  " Using either "o" or "O" repeats a line comment occupying a whole line.
+  %del
+  let text =<< trim END
+      nop;
+      // This is a comment
+      val = val;
+  END
+  call setline(1, text)
+  normal 2Go
+  let expected =<< trim END
+      nop;
+      // This is a comment
+      //
+      val = val;
+  END
+  call assert_equal(expected, getline(1, '$'))
+  normal 2GO
+  let expected =<< trim END
+      nop;
+      //
+      // This is a comment
+      //
+      val = val;
+  END
+  call assert_equal(expected, getline(1, '$'))
+
+  " Using "o" repeats a line comment after a statement, "O" does not.
   %del
   let text =<< trim END
       nop;