1 files changed, 31 insertions, 1 deletions

diff --git a/src/w32proc.c b/src/w32proc.c
index 961791a40ed..84589388cd7 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -2263,12 +2263,42 @@ sys_kill (pid_t pid, int sig)
     pid = -pid;
 
   /* Only handle signals that will result in the process dying */
-  if (sig != SIGINT && sig != SIGKILL && sig != SIGQUIT && sig != SIGHUP)
+  if (sig != 0
+      && sig != SIGINT && sig != SIGKILL && sig != SIGQUIT && sig != SIGHUP)
     {
       errno = EINVAL;
       return -1;
     }
 
+  if (sig == 0)
+    {
+      /* It will take _some_ time before PID 4 or less on Windows will
+         be Emacs...  */
+      if (pid <= 4)
+        {
+          errno = EPERM;
+          return -1;
+        }
+      proc_hand = OpenProcess (PROCESS_QUERY_INFORMATION, 0, pid);
+      if (proc_hand == NULL)
+        {
+          DWORD err = GetLastError ();
+
+          switch (err)
+            {
+            case ERROR_ACCESS_DENIED: /* existing process, but access denied */
+              errno = EPERM;
+              return -1;
+            case ERROR_INVALID_PARAMETER: /* process PID does not exist */
+              errno = ESRCH;
+              return -1;
+            }
+        }
+      else
+        CloseHandle (proc_hand);
+      return 0;
+    }
+
   cp = find_child_pid (pid);
   if (cp == NULL)
     {