diff --git a/CHANGES b/CHANGES
index e54fc8c..5f9811a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -30,6 +30,10 @@ Coding:
 	starting the data transfer loop. Useful, e.g., to accumulate multiple
 	packets in a receiving datagram socket before starting to process them.
 
+Porting:
+	Small correction in configure.ac makes Socat C99 able.
+	Thanks to Florian Weimer from Red Hat for provinding a patch.
+
 Testing:
 	Idea: EXEC,SYSTEM addresses can keep packet boundaries when option
 	socktype=<val-of-SOCK_DGRAM>
diff --git a/configure.ac b/configure.ac
index 9d60473..c5aabd2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -582,7 +582,9 @@ if test -n "$WITH_OPENSSL" -a "$sc_cv_have_openssl_ssl_h" = 'yes'; then
       else
 	LIBS="$LIBS -lssl -lcrypto"
       fi
-      AC_TRY_LINK([#include <openssl/ssl.h>],
+      AC_TRY_LINK([#include <openssl/ssl.h>
+      #include <openssl/err.h>
+      ],
        [SSL_library_init();ERR_error_string()],
        [sc_cv_have_libssl='yes'],
        [ LIBS="$LIBS -lcrypto"