diff --git a/src/testdir/test_termcodes.vim b/src/testdir/test_termcodes.vim
index 27c2a18..a267696 100644
--- a/src/testdir/test_termcodes.vim
+++ b/src/testdir/test_termcodes.vim
@@ -194,9 +194,10 @@
   new
   let save_mouse = &mouse
   let save_term = &term
+  let save_wrap = &wrap
   let save_ttymouse = &ttymouse
-  set mouse=a term=xterm
-  call setline(1, range(1, 100))
+  set mouse=a term=xterm nowrap
+  call setline(1, range(100000000000000, 100000000000100))
 
   for ttymouse_val in g:Ttymouse_values
     let msg = 'ttymouse=' .. ttymouse_val
@@ -220,10 +221,31 @@
     call MouseWheelUp(1, 1)
     call assert_equal(1, line('w0'), msg)
     call assert_equal([0, 7, 1, 0], getpos('.'), msg)
+
+    if has('gui')
+      " Horizontal wheel scrolling currently only works when vim is
+      " compiled with gui enabled.
+      call MouseWheelRight(1, 1)
+      call assert_equal(7, 1 + virtcol(".") - wincol(), msg)
+      call assert_equal([0, 7, 7, 0], getpos('.'), msg)
+
+      call MouseWheelRight(1, 1)
+      call assert_equal(13, 1 + virtcol(".") - wincol(), msg)
+      call assert_equal([0, 7, 13, 0], getpos('.'), msg)
+
+      call MouseWheelLeft(1, 1)
+      call assert_equal(7, 1 + virtcol(".") - wincol(), msg)
+      call assert_equal([0, 7, 13, 0], getpos('.'), msg)
+
+      call MouseWheelLeft(1, 1)
+      call assert_equal(1, 1 + virtcol(".") - wincol(), msg)
+      call assert_equal([0, 7, 13, 0], getpos('.'), msg)
+    endif
   endfor
 
   let &mouse = save_mouse
   let &term = save_term
+  let &wrap = save_wrap
   let &ttymouse = save_ttymouse
   bwipe!
 endfunc