diff --git a/libguile/posix.c b/libguile/posix.c
index a96dabcfa..4b598103b 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -156,6 +156,11 @@ extern char ** environ;
 #define F_OK 0
 #endif
 
+/* No prototype for this on Solaris 10. */
+#if ! HAVE_DECL_SETHOSTNAME
+int sethostname (char *name, size_t namelen);
+#endif
+
 /* On NextStep, <utime.h> doesn't define struct utime, unless we
    #define _POSIX_SOURCE before #including it.  I think this is less
    of a kludge than defining struct utimbuf ourselves.  */