diff --git a/CHANGES b/CHANGES
index 1941793..7303704 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2,7 +2,13 @@
 Corrections:
 	Socat 1.7.4.2 did not compile on OmniOS (and probably other OpenSolaris
 	distributions)
-	Thanks to Andy Fiddaman for sending a patch
+	Thanks to Andy Fiddaman for sending a patch.
+
+	Socat since 1.7.4.0 did not compile on Solaris and its derivatives
+	because the getprotobynumber_r() function prototype differ from the
+	Linux versino.
+	configure now checks for the variant.
+	Thanks to Robert Zybeck for reporting this issue.
 
 ####################### V 1.7.4.2:
 
diff --git a/configure.ac b/configure.ac
index 09dbb7a..afbc534 100644
--- a/configure.ac
+++ b/configure.ac
@@ -134,6 +134,23 @@ if test $sc_cv_have_prototype_hstrerror = yes; then
 fi
 AC_MSG_RESULT($sc_cv_have_prototype_hstrerror)
 
+# getprotobynumber_r() is not standardized
+AC_MSG_CHECKING(for getprotobynumber_r() variant)
+AC_CACHE_VAL(sc_cv_getprotobynumber_r,
+[AC_TRY_COMPILE([#include <stddef.h>
+#include <netdb.h>],[getprotobynumber_r(1,NULL,NULL,1024,NULL);],
+[sc_cv_getprotobynumber_r=1; tmp_bynum_variant=Linux],
+ [AC_TRY_COMPILE([#include <stddef.h>
+ #include <netdb.h>],[getprotobynumber_r(1,NULL,NULL,1024);],
+ [sc_cv_getprotobynumber_r=2; tmp_bynum_variant=Solaris],
+ # there is a 3 arg variant in AIX, but its doc is limited
+ [sc_cv_getprotobynumber_r=]
+)])])
+if test "$sc_cv_getprotobynumber_r"; then
+   AC_DEFINE_UNQUOTED(HAVE_GETPROTOBYNUMBER_R, $sc_cv_getprotobynumber_r)
+fi
+AC_MSG_RESULT($sc_cv_getprotobynumber_r /* $tmp_bynum_variant */)
+
 
 AC_MSG_CHECKING(whether to include help)
 AC_ARG_ENABLE(help, [  --disable-help          disable help],
@@ -811,7 +828,7 @@ AC_TYPE_SIGNAL
 AC_FUNC_STRFTIME
 AC_CHECK_FUNCS(putenv select pselect poll socket strtod strtol)
 AC_CHECK_FUNCS(strtoul uname getpgid getsid gethostbyname getaddrinfo)
-AC_CHECK_FUNCS(getprotobynumber getprotobynumber_r)
+AC_CHECK_FUNCS(getprotobynumber)
 AC_CHECK_FUNCS(setgroups inet_aton)
 
 AC_CHECK_FUNCS(grantpt unlockpt)
diff --git a/fdname.c b/fdname.c
index 3f2c449..ee1d5ce 100644
--- a/fdname.c
+++ b/fdname.c
@@ -253,14 +253,14 @@ int sockname(int fd, FILE *outfile, char style) {
 #endif
 
 #if defined(SO_PROTOCOL) || defined(SO_PROTOTYPE)
-#if HAVE_GETPROTOBYNUMBER_R
+#if HAVE_GETPROTOBYNUMBER_R==1 /* Linux */
    rc = getprotobynumber_r(proto, &protoent, protoname, sizeof(protoname), &protoentp);
    if (protoentp == NULL) {
       Warn2("sockname(): getprotobynumber_r(proto=%d, ...): %s",
 	    proto, strerror(rc));
    }
    strncpy(protoname, protoentp->p_name, sizeof(protoname));
-#elif HAVE_GETPROTOBYNUMBER
+#elif HAVE_GETPROTOBYNUMBER_R==2 /* Solaris */
    protoentp = getprotobynumber(proto);
    strncpy(protoname, protoentp->p_name, sizeof(protoname));
 #else