diff --git a/src/testdir/test_writefile.vim b/src/testdir/test_writefile.vim
index 2e47b48..ff36756 100644
--- a/src/testdir/test_writefile.vim
+++ b/src/testdir/test_writefile.vim
@@ -33,7 +33,7 @@
 endfunc
 
 func Test_writefile_fails_conversion()
-  if !has('iconv') || system('uname -s') =~ 'SunOS'
+  if !has('iconv') || has('sun')
     return
   endif
   set nobackup nowritebackup