diff --git a/ChangeLog b/ChangeLog
index ecbf272dc..27e9198c8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -56,6 +56,10 @@ Bugfix
    * Don't print X.509 version tag for v1 CRT's, and omit extensions for
      non-v3 CRT's.
    * Fix bugs in RSA test suite under MBEDTLS_NO_PLATFORM_ENTROPY. #1023 #1024
+   * Fix net_would_block to avoid modification by errno through fcntl call.
+     Found by nkolban. Fixes #845.
+   * Fix handling of handshake messages in ssl_read in case
+     POLARSSL_SSL_DISABLE_RENEGOTIATION is set. Found by erja-gp.
 
 Changes
    * Extend cert_write example program by options to set the CRT version
diff --git a/library/net.c b/library/net.c
index b42b86f81..ad57c6a65 100644
--- a/library/net.c
+++ b/library/net.c
@@ -404,13 +404,18 @@ static int net_would_block( int fd )
  */
 static int net_would_block( int fd )
 {
+    int err = errno;
+
     /*
      * Never return 'WOULD BLOCK' on a non-blocking socket
      */
     if( ( fcntl( fd, F_GETFL ) & O_NONBLOCK ) != O_NONBLOCK )
+    {
+        errno = err;
         return( 0 );
+    }
 
-    switch( errno )
+    switch( errno = err )
     {
 #if defined EAGAIN
         case EAGAIN:
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index eaf50be28..b08e490fb 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4762,7 +4762,6 @@ int ssl_read( ssl_context *ssl, unsigned char *buf, size_t len )
             }
         }
 
-#if defined(POLARSSL_SSL_RENEGOTIATION)
         if( ssl->in_msgtype == SSL_MSG_HANDSHAKE )
         {
             SSL_DEBUG_MSG( 1, ( "received handshake message" ) );
@@ -4777,10 +4776,22 @@ int ssl_read( ssl_context *ssl, unsigned char *buf, size_t len )
             }
 #endif
 
-            if( ssl->disable_renegotiation == SSL_RENEGOTIATION_DISABLED ||
-                ( ssl->secure_renegotiation == SSL_LEGACY_RENEGOTIATION &&
-                  ssl->allow_legacy_renegotiation ==
-                                                SSL_LEGACY_NO_RENEGOTIATION ) )
+#if defined(POLARSSL_SSL_RENEGOTIATION)
+            if( ! ( ssl->disable_renegotiation == SSL_RENEGOTIATION_DISABLED ||
+                    ( ssl->secure_renegotiation == SSL_LEGACY_RENEGOTIATION &&
+                      ssl->allow_legacy_renegotiation ==
+                                                   SSL_LEGACY_NO_RENEGOTIATION ) ) )
+            {
+                ret = ssl_start_renegotiation( ssl );
+                if( ret != POLARSSL_ERR_SSL_WAITING_SERVER_HELLO_RENEGO &&
+                    ret != 0 )
+                {
+                    SSL_DEBUG_RET( 1, "ssl_start_renegotiation", ret );
+                    return( ret );
+                }
+            }
+            else
+#endif /* POLARSSL_SSL_RENEGOTIATION */
             {
                 SSL_DEBUG_MSG( 3, ( "ignoring renegotiation, sending alert" ) );
 
@@ -4814,19 +4825,10 @@ int ssl_read( ssl_context *ssl, unsigned char *buf, size_t len )
                     return( POLARSSL_ERR_SSL_INTERNAL_ERROR );
                 }
             }
-            else
-            {
-                ret = ssl_start_renegotiation( ssl );
-                if( ret != POLARSSL_ERR_SSL_WAITING_SERVER_HELLO_RENEGO &&
-                    ret != 0 )
-                {
-                    SSL_DEBUG_RET( 1, "ssl_start_renegotiation", ret );
-                    return( ret );
-                }
-            }
 
             return( POLARSSL_ERR_NET_WANT_READ );
         }
+#if defined(POLARSSL_SSL_RENEGOTIATION)
         else if( ssl->renegotiation == SSL_RENEGOTIATION_PENDING )
         {
             ssl->renego_records_seen++;
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 133d98677..cb255c476 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -259,6 +259,19 @@ OPENSSL_CMD="$OPENSSL_LEGACY" tests/compat.sh -m 'ssl3'
 msg "build: SSLv3 - ssl-opt.sh (ASan build)" # ~ 6 min
 tests/ssl-opt.sh
 
+msg "build: Default + POLARSSL_SSL_DISABLE_RENEGOTIATION (ASan build)" # ~ 6 min
+cleanup
+cp "$CONFIG_H" "$CONFIG_BAK"
+scripts/config.pl set POLARSSL_SSL_DISABLE_RENEGOTIATION
+CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan .
+make
+
+msg "test: POLARSSL_SSL_DISABLE_RENEGOTIATION - main suites (inc. selftests) (ASan build)" # ~ 50s
+make test
+
+msg "test: POLARSSL_SSL_DISABLE_RENEGOTIATION - ssl-opt.sh (ASan build)" # ~ 6 min
+tests/ssl-opt.sh
+
 msg "build: cmake, full config, clang" # ~ 50s
 cleanup
 cp "$CONFIG_H" "$CONFIG_BAK"
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 0f976682b..51d31fdfd 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -75,6 +75,13 @@ requires_config_enabled() {
     fi
 }
 
+# skip next test if the flag is enabled in config.h
+requires_config_disabled() {
+    if grep "^#define $1" $CONFIG_H > /dev/null; then
+        SKIP_NEXT="YES"
+    fi
+}
+
 # skip next test if OpenSSL can't send SSLv2 ClientHello
 requires_openssl_with_sslv2() {
     if [ -z "${OPENSSL_HAS_SSL2:-}" ]; then
@@ -1073,6 +1080,7 @@ run_test    "Renegotiation: none, for reference" \
             -S "=> renegotiate" \
             -S "write hello request"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: client-initiated" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1086,6 +1094,7 @@ run_test    "Renegotiation: client-initiated" \
             -s "=> renegotiate" \
             -S "write hello request"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: server-initiated" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1" \
@@ -1102,6 +1111,7 @@ run_test    "Renegotiation: server-initiated" \
 # Checks that no Signature Algorithm with SHA-1 gets negotiated. Negotiating SHA-1 would mean that
 # the server did not parse the Signature Algorithm extension. This test is valid only if an MD
 # algorithm stronger than SHA-1 is enabled in config.h
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: Signature Algorithms parsing, client-initiated" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1119,6 +1129,7 @@ run_test    "Renegotiation: Signature Algorithms parsing, client-initiated" \
 # Checks that no Signature Algorithm with SHA-1 gets negotiated. Negotiating SHA-1 would mean that
 # the server did not parse the Signature Algorithm extension. This test is valid only if an MD
 # algorithm stronger than SHA-1 is enabled in config.h
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: Signature Algorithms parsing, server-initiated" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 auth_mode=optional renegotiate=1" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1" \
@@ -1133,6 +1144,7 @@ run_test    "Renegotiation: Signature Algorithms parsing, server-initiated" \
             -s "write hello request" \
             -S "client hello v3, signature_algorithm ext: 2" # Is SHA-1 negotiated?
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: double" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1146,6 +1158,7 @@ run_test    "Renegotiation: double" \
             -s "=> renegotiate" \
             -s "write hello request"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: client-initiated, server-rejected" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=0" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1161,6 +1174,7 @@ run_test    "Renegotiation: client-initiated, server-rejected" \
             -c "SSL - Unexpected message at ServerHello in renegotiation" \
             -c "failed"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, default" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=0" \
@@ -1176,6 +1190,7 @@ run_test    "Renegotiation: server-initiated, client-rejected, default" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, not enforced" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=-1" \
@@ -1193,6 +1208,7 @@ run_test    "Renegotiation: server-initiated, client-rejected, not enforced" \
             -S "failed"
 
 # delay 2 for 1 alert record + 1 application data record
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, delay 2" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=2" \
@@ -1209,6 +1225,7 @@ run_test    "Renegotiation: server-initiated, client-rejected, delay 2" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, delay 0" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=0" \
@@ -1224,6 +1241,7 @@ run_test    "Renegotiation: server-initiated, client-rejected, delay 0" \
             -s "write hello request" \
             -s "SSL - An unexpected message was received from our peer"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-accepted, delay 0" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=0" \
@@ -1240,6 +1258,7 @@ run_test    "Renegotiation: server-initiated, client-accepted, delay 0" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: periodic, just below period" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=1 renego_period=3" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1" \
@@ -1257,6 +1276,7 @@ run_test    "Renegotiation: periodic, just below period" \
             -S "failed"
 
 # one extra exchange to be able to complete renego
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: periodic, just above period" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=1 renego_period=3" \
             "$P_CLI debug_level=3 exchanges=4 renegotiation=1" \
@@ -1273,6 +1293,7 @@ run_test    "Renegotiation: periodic, just above period" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: periodic, two times period" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=1 renego_period=3" \
             "$P_CLI debug_level=3 exchanges=7 renegotiation=1" \
@@ -1289,6 +1310,7 @@ run_test    "Renegotiation: periodic, two times period" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: periodic, above period, disabled" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=0 renego_period=3" \
             "$P_CLI debug_level=3 exchanges=4 renegotiation=1" \
@@ -1305,6 +1327,7 @@ run_test    "Renegotiation: periodic, above period, disabled" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: nbio, client-initiated" \
             "$P_SRV debug_level=3 nbio=2 exchanges=2 renegotiation=1" \
             "$P_CLI debug_level=3 nbio=2 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1318,6 +1341,7 @@ run_test    "Renegotiation: nbio, client-initiated" \
             -s "=> renegotiate" \
             -S "write hello request"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: nbio, server-initiated" \
             "$P_SRV debug_level=3 nbio=2 exchanges=2 renegotiation=1 renegotiate=1" \
             "$P_CLI debug_level=3 nbio=2 exchanges=2 renegotiation=1" \
@@ -1331,6 +1355,7 @@ run_test    "Renegotiation: nbio, server-initiated" \
             -s "=> renegotiate" \
             -s "write hello request"
 
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: openssl server, client-initiated" \
             "$O_SRV" \
             "$P_CLI debug_level=3 exchanges=1 renegotiation=1 renegotiate=1" \
@@ -1343,6 +1368,7 @@ run_test    "Renegotiation: openssl server, client-initiated" \
             -c "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: gnutls server strict, client-initiated" \
             "$G_SRV --priority=NORMAL:%SAFE_RENEGOTIATION" \
             "$P_CLI debug_level=3 exchanges=1 renegotiation=1 renegotiate=1" \
@@ -1355,6 +1381,7 @@ run_test    "Renegotiation: gnutls server strict, client-initiated" \
             -c "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: gnutls server unsafe, client-initiated default" \
             "$G_SRV --priority=NORMAL:%DISABLE_SAFE_RENEGOTIATION" \
             "$P_CLI debug_level=3 exchanges=1 renegotiation=1 renegotiate=1" \
@@ -1367,6 +1394,7 @@ run_test    "Renegotiation: gnutls server unsafe, client-initiated default" \
             -C "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: gnutls server unsafe, client-inititated no legacy" \
             "$G_SRV --priority=NORMAL:%DISABLE_SAFE_RENEGOTIATION" \
             "$P_CLI debug_level=3 exchanges=1 renegotiation=1 renegotiate=1 \
@@ -1380,6 +1408,7 @@ run_test    "Renegotiation: gnutls server unsafe, client-inititated no legacy" \
             -C "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_disabled POLARSSL_SSL_DISABLE_RENEGOTIATION
 run_test    "Renegotiation: gnutls server unsafe, client-inititated legacy" \
             "$G_SRV --priority=NORMAL:%DISABLE_SAFE_RENEGOTIATION" \
             "$P_CLI debug_level=3 exchanges=1 renegotiation=1 renegotiate=1 \