diff --git a/src/testdir/test_assert.vim b/src/testdir/test_assert.vim
index d7fb638..0ab664a 100644
--- a/src/testdir/test_assert.vim
+++ b/src/testdir/test_assert.vim
@@ -105,6 +105,19 @@
   call remove(v:errors, 0)
 endfunc
 
+func Test_assert_inrange()
+  call assert_inrange(7, 7, 7)
+  call assert_inrange(5, 7, 5)
+  call assert_inrange(5, 7, 6)
+  call assert_inrange(5, 7, 7)
+
+  call assert_inrange(5, 7, 4)
+  call assert_match("Expected range 5 - 7, but got 4", v:errors[0])
+  call remove(v:errors, 0)
+  call assert_inrange(5, 7, 8)
+  call assert_match("Expected range 5 - 7, but got 8", v:errors[0])
+  call remove(v:errors, 0)
+endfunc
 
 func Test_user_is_happy()
   smile
diff --git a/src/testdir/test_man.vim b/src/testdir/test_man.vim
index f2c48a4..1485ec3 100644
--- a/src/testdir/test_man.vim
+++ b/src/testdir/test_man.vim
@@ -1,19 +1,20 @@
 runtime ftplugin/man.vim
 
 function Test_g_ft_man_open_mode()
-  let l:w = winwidth(1)
   vnew
   let l:h = winheight(1)
   q
+  let l:w = winwidth(1)
 
   " split horizontally
   let wincnt = winnr('$')
-  Man 'vim'
+  Man vim
   if wincnt == winnr('$')
     " Vim manual page cannot be found.
     return
   endif
-  call assert_equal(l:w, winwidth(1))
+
+  call assert_inrange(l:w - 2, l:w + 2, winwidth(1))
   call assert_true(l:h > winheight(1))
   call assert_equal(1, tabpagenr('$'))
   call assert_equal(1, tabpagenr())
@@ -21,8 +22,8 @@
 
   " split horizontally
   let g:ft_man_open_mode = "horz"
-  Man 'vim'
-  call assert_equal(l:w, winwidth(1))
+  Man vim
+  call assert_inrange(l:w - 2, l:w + 2, winwidth(1))
   call assert_true(l:h > winheight(1))
   call assert_equal(1, tabpagenr('$'))
   call assert_equal(1, tabpagenr())
@@ -30,7 +31,7 @@
 
   " split vertically
   let g:ft_man_open_mode = "vert"
-  Man 'vim'
+  Man vim
   call assert_true(l:w > winwidth(1))
   call assert_equal(l:h, winheight(1))
   call assert_equal(1, tabpagenr('$'))
@@ -39,9 +40,9 @@
 
   " separate tab
   let g:ft_man_open_mode = "tab"
-  Man 'vim'
-  call assert_equal(l:w, winwidth(1))
-  call assert_equal(l:h, winheight(1))
+  Man vim
+  call assert_inrange(l:w - 2, l:w + 2, winwidth(1))
+  call assert_inrange(l:h - 1, l:h + 1, winheight(1))
   call assert_equal(2, tabpagenr('$'))
   call assert_equal(2, tabpagenr())
   q
@@ -49,7 +50,7 @@
 
 function Test_nomodifiable()
   let wincnt = winnr('$')
-  Man 'vim'
+  Man vim
   if wincnt == winnr('$')
     " Vim manual page cannot be found.
     return