diff --git a/src/callproc.c b/src/callproc.c
index 4b674eb9946..72d2b8c6ddd 100644
--- a/src/callproc.c
+++ b/src/callproc.c
@@ -151,11 +151,7 @@ If you quit, the process is killed with SIGINT, or SIGKILL if you quit again.")
       CHECK_STRING (infile, 1);
     }
   else
-#ifdef VMS
-    infile = build_string ("NLA0:");
-#else
-    infile = build_string ("/dev/null");
-#endif /* not VMS */
+    infile = build_string (NULL_DEVICE);
 
   if (nargs >= 3)
     {
@@ -220,7 +216,7 @@ If you quit, the process is killed with SIGINT, or SIGKILL if you quit again.")
       report_file_error ("Opening process input file", Fcons (infile, Qnil));
     }
   /* Search for program; barf if not found.  */
-  openp (Vexec_path, args[0], "", &path, 1);
+  openp (Vexec_path, args[0], EXEC_SUFFIXES, &path, 1);
   if (NILP (path))
     {
       close (filefd);
@@ -229,7 +225,7 @@ If you quit, the process is killed with SIGINT, or SIGKILL if you quit again.")
   new_argv[0] = XSTRING (path)->data;
 
   if (XTYPE (buffer) == Lisp_Int)
-    fd[1] = open ("/dev/null", O_WRONLY), fd[0] = -1;
+    fd[1] = open (NULL_DEVICE, O_WRONLY), fd[0] = -1;
   else
     {
       pipe (fd);
diff --git a/src/process.c b/src/process.c
index ed80460286a..d52f52bcdfd 100644
--- a/src/process.c
+++ b/src/process.c
@@ -1034,7 +1034,7 @@ Remaining arguments are strings to give program as arguments.")
   if (new_argv[0][0] != '/')
     {
       tem = Qnil;
-      openp (Vexec_path, program, "", &tem, 1);
+      openp (Vexec_path, program, EXEC_SUFFIXES, &tem, 1);
       if (NILP (tem))
 	report_file_error ("Searching for program", Fcons (program, Qnil));
       new_argv[0] = XSTRING (tem)->data;
@@ -2597,7 +2597,7 @@ nil, indicating the current buffer's process.")
   else
     {
       close (XPROCESS (proc)->outfd);
-      XFASTINT (XPROCESS (proc)->outfd) = open ("/dev/null", O_WRONLY);
+      XFASTINT (XPROCESS (proc)->outfd) = open (NULL_DEVICE, O_WRONLY);
     }
 #endif /* VMS */
 #endif /* did not do TOICREMOTE */
diff --git a/src/process.h b/src/process.h
index 8f476f6894d..2ac7b59c6b7 100644
--- a/src/process.h
+++ b/src/process.h
@@ -91,3 +91,14 @@ extern char *synch_process_death;
    this is exit code of synchronous subprocess.  */
 extern int synch_process_retcode;
 
+/* The name of the file open to get a null file, or a data sink.
+   VMS, MS-DOS, and OS/2 redefine this.  */
+#ifndef NULL_DEVICE
+#define NULL_DEVICE "/dev/null"
+#endif
+
+/* A string listing the possible suffixes used for executable files,
+   separated by colons.  VMS, MS-DOS, and OS/2 redefine this.  */
+#ifndef EXEC_SUFFIXES
+#define EXEC_SUFFIXES ""
+#endif