diff --git a/windows/winnet.c b/windows/winnet.c
index ab38e547..ae0a364f 100644
--- a/windows/winnet.c
+++ b/windows/winnet.c
@@ -845,7 +845,7 @@ static const SocketVtable NetSocket_sockvt = {
 static Socket *sk_net_accept(accept_ctx_t ctx, Plug *plug)
 {
     DWORD err;
-    char *errstr;
+    const char *errstr;
     NetSocket *ret;
 
     /*
@@ -897,7 +897,7 @@ static DWORD try_connect(NetSocket *sock)
 #endif
     SOCKADDR_IN a;
     DWORD err;
-    char *errstr;
+    const char *errstr;
     short localport;
     int family;
 
@@ -1137,7 +1137,7 @@ Socket *sk_newlistener(const char *srcaddr, int port, Plug *plug,
     SOCKADDR_IN a;
 
     DWORD err;
-    char *errstr;
+    const char *errstr;
     NetSocket *ret;
     int retcode;
 
diff --git a/windows/winselcli.c b/windows/winselcli.c
index c19706d7..f19a0bbe 100644
--- a/windows/winselcli.c
+++ b/windows/winselcli.c
@@ -45,7 +45,7 @@ SOCKET winselcli_unique_socket(void)
     return *p;
 }
 
-char *do_select(SOCKET skt, bool enable)
+const char *do_select(SOCKET skt, bool enable)
 {
     /* Check everything's been set up, for convenience of callers. */
     winselcli_setup();
diff --git a/windows/winselgui.c b/windows/winselgui.c
index 1dc376bd..48a15212 100644
--- a/windows/winselgui.c
+++ b/windows/winselgui.c
@@ -18,7 +18,7 @@ void winselgui_clear_hwnd(void)
     winsel_hwnd = NULL;
 }
 
-char *do_select(SOCKET skt, bool enable)
+const char *do_select(SOCKET skt, bool enable)
 {
     int msg, events;
     if (enable) {
diff --git a/windows/winstuff.h b/windows/winstuff.h
index 1870b28e..5acd215f 100644
--- a/windows/winstuff.h
+++ b/windows/winstuff.h
@@ -352,7 +352,7 @@ DECL_WINDOWS_FUNCTION(GLOBAL, int, select,
  * Implemented differently depending on the client of winnet.c, and
  * called by winnet.c to turn on or off WSA*Select for a given socket.
  */
-char *do_select(SOCKET skt, bool enable);
+const char *do_select(SOCKET skt, bool enable);
 
 /*
  * Exports from winselgui.c and winselcli.c, each of which provides an