diff --git a/src/testdir/test_clientserver.vim b/src/testdir/test_clientserver.vim
index 58ced56..86dad54 100644
--- a/src/testdir/test_clientserver.vim
+++ b/src/testdir/test_clientserver.vim
@@ -11,13 +11,15 @@
   if cmd == ''
     return
   endif
-  if has('unix')
+  if has('x11')
+    if empty($DISPLAY)
+      throw 'Skipped: $DISPLAY is not set'
+    endif
     try
       call remote_send('xxx', '')
     catch
       if v:exception =~ 'E240:'
-	" No connection to the X server, give up.
-	return
+	throw 'Skipped: no connection to the X server'
       endif
       " ignore other errors
     endtry
diff --git a/src/testdir/test_quotestar.vim b/src/testdir/test_quotestar.vim
index 6e4e4ca..37e3a10 100644
--- a/src/testdir/test_quotestar.vim
+++ b/src/testdir/test_quotestar.vim
@@ -118,8 +118,12 @@
 
   if has('macunix')
     let skipped = Do_test_quotestar_for_macunix()
-  elseif !empty("$DISPLAY")
-    let skipped = Do_test_quotestar_for_x11()
+  elseif has('x11')
+    if empty($DISPLAY)
+      let skipped = "Test can only run when $DISPLAY is set."
+    else
+      let skipped = Do_test_quotestar_for_x11()
+    endif
   else
     let skipped = "Test is not implemented yet for this platform."
   endif
diff --git a/src/version.c b/src/version.c
index 08adb69..7d2cf27 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    511,
+/**/
     510,
 /**/
     509,