diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index b76bc78..7efbbe8 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -948,3 +948,39 @@
   delfunc s:save_reg_stat
   unlet s:reg_stat
 endfunc
+
+func Test_libcall_libcallnr()
+  if !has('libcall')
+    return
+  endif
+
+  if has('win32')
+    let libc = 'msvcrt.dll'
+  elseif has('mac')
+    let libc = 'libSystem.B.dylib'
+  else
+    " On Unix, libc.so can be in various places.
+    " Interestingly, using an empty string for the 1st argument of libcall
+    " allows to call functions from libc which is not documented.
+    let libc = ''
+  endif
+
+  if has('win32')
+    call assert_equal($USERPROFILE, libcall(libc, 'getenv', 'USERPROFILE'))
+  else
+    call assert_equal($HOME, libcall(libc, 'getenv', 'HOME'))
+  endif
+
+  " If function returns NULL, libcall() should return an empty string.
+  call assert_equal('', libcall(libc, 'getenv', 'X_ENV_DOES_NOT_EXIT'))
+
+  " Test libcallnr() with string and integer argument.
+  call assert_equal(4, libcallnr(libc, 'strlen', 'abcd'))
+  call assert_equal(char2nr('A'), libcallnr(libc, 'toupper', char2nr('a')))
+
+  call assert_fails("call libcall(libc, 'Xdoesnotexist_', '')", 'E364:')
+  call assert_fails("call libcallnr(libc, 'Xdoesnotexist_', '')", 'E364:')
+
+  call assert_fails("call libcall('Xdoesnotexist_', 'getenv', 'HOME')", 'E364:')
+  call assert_fails("call libcallnr('Xdoesnotexist_', 'strlen', 'abcd')", 'E364:')
+endfunc