diff --git a/src/process.c b/src/process.c
index 7d3cf19d57f..a60814b2386 100644
--- a/src/process.c
+++ b/src/process.c
@@ -138,7 +138,7 @@ static struct rlimit nofile_limit;
 
 #ifdef WINDOWSNT
 extern int sys_select (int, fd_set *, fd_set *, fd_set *,
-                       struct timespec *, sigset_t *);
+                       const struct timespec *, const sigset_t *);
 #endif
 
 /* Work around GCC 4.3.0 bug with strict overflow checking; see
diff --git a/src/thread.h b/src/thread.h
index 64448007531..a9de754d6b4 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -226,7 +226,7 @@ extern void init_threads (void);
 extern void syms_of_threads (void);
 
 typedef int select_func (int, fd_set *, fd_set *, fd_set *,
-			 struct timespec *, sigset_t *);
+			 const struct timespec *, const sigset_t *);
 
 int thread_select  (select_func *func, int max_fds, fd_set *rfds,
 		    fd_set *wfds, fd_set *efds, struct timespec *timeout,
diff --git a/src/w32.c b/src/w32.c
index 7a80275a7c8..c6fc7ef8567 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -272,7 +272,7 @@ static BOOL WINAPI revert_to_self (void);
 static int sys_access (const char *, int);
 extern void *e_malloc (size_t);
 extern int sys_select (int, SELECT_TYPE *, SELECT_TYPE *, SELECT_TYPE *,
-		       struct timespec *, sigset_t *);
+		       const struct timespec *, const sigset_t *);
 extern int sys_dup (int);
 
 
diff --git a/src/w32proc.c b/src/w32proc.c
index 3ff52c37fbd..6f3a6e0efca 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -72,7 +72,7 @@ extern BOOL g_b_init_compare_string_w;
 extern BOOL g_b_init_debug_break_process;
 
 int sys_select (int, SELECT_TYPE *, SELECT_TYPE *, SELECT_TYPE *,
-		struct timespec *, sigset_t *);
+		const struct timespec *, const sigset_t *);
 
 /* Signal handlers...SIG_DFL == 0 so this is initialized correctly.  */
 static signal_handler sig_handlers[NSIG];
@@ -2096,7 +2096,7 @@ extern int proc_buffered_char[];
 
 int
 sys_select (int nfds, SELECT_TYPE *rfds, SELECT_TYPE *wfds, SELECT_TYPE *efds,
-	    struct timespec *timeout, sigset_t *ignored)
+	    const struct timespec *timeout, const sigset_t *ignored)
 {
   SELECT_TYPE orfds, owfds;
   DWORD timeout_ms, start_time;