diff --git a/ChangeLog b/ChangeLog
index af8079c67..6d1ec368e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -64,6 +64,10 @@ 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 mbedtls_ssl_read in case
+     MBEDTLS_SSL_RENEGOTIATION is disabled. 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 b6b08ed72..f08bbec51 100644
--- a/library/net.c
+++ b/library/net.c
@@ -259,13 +259,18 @@ static int net_would_block( const mbedtls_net_context *ctx )
  */
 static int net_would_block( const mbedtls_net_context *ctx )
 {
+    int err = errno;
+    
     /*
      * Never return 'WOULD BLOCK' on a non-blocking socket
      */
     if( ( fcntl( ctx->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 1c4540743..7ceee4d6d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -6657,7 +6657,6 @@ int mbedtls_ssl_read( mbedtls_ssl_context *ssl, unsigned char *buf, size_t len )
             }
         }
 
-#if defined(MBEDTLS_SSL_RENEGOTIATION)
         if( ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE )
         {
             MBEDTLS_SSL_DEBUG_MSG( 1, ( "received handshake message" ) );
@@ -6693,10 +6692,30 @@ int mbedtls_ssl_read( mbedtls_ssl_context *ssl, unsigned char *buf, size_t len )
             }
 #endif
 
-            if( ssl->conf->disable_renegotiation == MBEDTLS_SSL_RENEGOTIATION_DISABLED ||
-                ( ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
-                  ssl->conf->allow_legacy_renegotiation ==
-                                                MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION ) )
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+            if( ! ( ssl->conf->disable_renegotiation == MBEDTLS_SSL_RENEGOTIATION_DISABLED ||
+                    ( ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
+                      ssl->conf->allow_legacy_renegotiation ==
+                                                   MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION ) ) )
+            {
+                /* DTLS clients need to know renego is server-initiated */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+                if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+                    ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
+                {
+                    ssl->renego_status = MBEDTLS_SSL_RENEGOTIATION_PENDING;
+                }
+#endif
+                ret = ssl_start_renegotiation( ssl );
+                if( ret != MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO &&
+                    ret != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_RET( 1, "ssl_start_renegotiation", ret );
+                    return( ret );
+                }
+            }
+            else
+#endif /* MBEDTLS_SSL_RENEGOTIATION */
             {
                 MBEDTLS_SSL_DEBUG_MSG( 3, ( "refusing renegotiation, sending alert" ) );
 
@@ -6730,27 +6749,10 @@ int mbedtls_ssl_read( mbedtls_ssl_context *ssl, unsigned char *buf, size_t len )
                     return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
                 }
             }
-            else
-            {
-                /* DTLS clients need to know renego is server-initiated */
-#if defined(MBEDTLS_SSL_PROTO_DTLS)
-                if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
-                    ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
-                {
-                    ssl->renego_status = MBEDTLS_SSL_RENEGOTIATION_PENDING;
-                }
-#endif
-                ret = ssl_start_renegotiation( ssl );
-                if( ret != MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO &&
-                    ret != 0 )
-                {
-                    MBEDTLS_SSL_DEBUG_RET( 1, "ssl_start_renegotiation", ret );
-                    return( ret );
-                }
-            }
 
             return( MBEDTLS_ERR_SSL_WANT_READ );
         }
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
         else if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING )
         {
             if( ssl->conf->renego_max_records >= 0 )
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index f0594a25e..692dd70cb 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -289,6 +289,19 @@ 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 + !MBEDTLS_SSL_RENEGOTIATION (ASan build)" # ~ 6 min
+cleanup
+cp "$CONFIG_H" "$CONFIG_BAK"
+scripts/config.pl unset MBEDTLS_SSL_RENEGOTIATION
+CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan .
+make
+
+msg "test: !MBEDTLS_SSL_RENEGOTIATION - main suites (inc. selftests) (ASan build)" # ~ 50s
+make test
+
+msg "test: !MBEDTLS_SSL_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 5f47bb5d9..ff1ab8535 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -1384,6 +1384,7 @@ run_test    "Renegotiation: none, for reference" \
             -S "=> renegotiate" \
             -S "write hello request"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: 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" \
@@ -1397,6 +1398,7 @@ run_test    "Renegotiation: client-initiated" \
             -s "=> renegotiate" \
             -S "write hello request"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: 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" \
@@ -1413,6 +1415,7 @@ 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_enabled MBEDTLS_SSL_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" \
@@ -1430,6 +1433,7 @@ 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_enabled MBEDTLS_SSL_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" \
@@ -1444,6 +1448,7 @@ 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_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: double" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 auth_mode=optional renegotiate=1" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1457,6 +1462,7 @@ run_test    "Renegotiation: double" \
             -s "=> renegotiate" \
             -s "write hello request"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: client-initiated, server-rejected" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=0 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1472,6 +1478,7 @@ run_test    "Renegotiation: client-initiated, server-rejected" \
             -c "SSL - Unexpected message at ServerHello in renegotiation" \
             -c "failed"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, default" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=0" \
@@ -1487,6 +1494,7 @@ run_test    "Renegotiation: server-initiated, client-rejected, default" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, not enforced" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=-1 auth_mode=optional" \
@@ -1504,6 +1512,7 @@ run_test    "Renegotiation: server-initiated, client-rejected, not enforced" \
             -S "failed"
 
 # delay 2 for 1 alert record + 1 application data record
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, delay 2" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=2 auth_mode=optional" \
@@ -1520,6 +1529,7 @@ run_test    "Renegotiation: server-initiated, client-rejected, delay 2" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-rejected, delay 0" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=0 auth_mode=optional" \
@@ -1535,6 +1545,7 @@ 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_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: server-initiated, client-accepted, delay 0" \
             "$P_SRV debug_level=3 exchanges=2 renegotiation=1 renegotiate=1 \
              renego_delay=0 auth_mode=optional" \
@@ -1551,6 +1562,7 @@ run_test    "Renegotiation: server-initiated, client-accepted, delay 0" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: periodic, just below period" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=1 renego_period=3 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=2 renegotiation=1" \
@@ -1568,6 +1580,7 @@ run_test    "Renegotiation: periodic, just below period" \
             -S "failed"
 
 # one extra exchange to be able to complete renego
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: periodic, just above period" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=1 renego_period=3 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=4 renegotiation=1" \
@@ -1584,6 +1597,7 @@ run_test    "Renegotiation: periodic, just above period" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: periodic, two times period" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=1 renego_period=3 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=7 renegotiation=1" \
@@ -1600,6 +1614,7 @@ run_test    "Renegotiation: periodic, two times period" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: periodic, above period, disabled" \
             "$P_SRV debug_level=3 exchanges=9 renegotiation=0 renego_period=3 auth_mode=optional" \
             "$P_CLI debug_level=3 exchanges=4 renegotiation=1" \
@@ -1616,6 +1631,7 @@ run_test    "Renegotiation: periodic, above period, disabled" \
             -S "SSL - An unexpected message was received from our peer" \
             -S "failed"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: nbio, client-initiated" \
             "$P_SRV debug_level=3 nbio=2 exchanges=2 renegotiation=1 auth_mode=optional" \
             "$P_CLI debug_level=3 nbio=2 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1629,6 +1645,7 @@ run_test    "Renegotiation: nbio, client-initiated" \
             -s "=> renegotiate" \
             -S "write hello request"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: nbio, server-initiated" \
             "$P_SRV debug_level=3 nbio=2 exchanges=2 renegotiation=1 renegotiate=1 auth_mode=optional" \
             "$P_CLI debug_level=3 nbio=2 exchanges=2 renegotiation=1" \
@@ -1642,6 +1659,7 @@ run_test    "Renegotiation: nbio, server-initiated" \
             -s "=> renegotiate" \
             -s "write hello request"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: openssl server, client-initiated" \
             "$O_SRV -www" \
             "$P_CLI debug_level=3 exchanges=1 renegotiation=1 renegotiate=1" \
@@ -1654,6 +1672,7 @@ run_test    "Renegotiation: openssl server, client-initiated" \
             -c "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_enabled MBEDTLS_SSL_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" \
@@ -1666,6 +1685,7 @@ run_test    "Renegotiation: gnutls server strict, client-initiated" \
             -c "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_enabled MBEDTLS_SSL_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" \
@@ -1678,6 +1698,7 @@ run_test    "Renegotiation: gnutls server unsafe, client-initiated default" \
             -C "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_enabled MBEDTLS_SSL_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 \
@@ -1691,6 +1712,7 @@ run_test    "Renegotiation: gnutls server unsafe, client-inititated no legacy" \
             -C "HTTP/1.0 200 [Oo][Kk]"
 
 requires_gnutls
+requires_config_enabled MBEDTLS_SSL_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 \
@@ -1703,6 +1725,7 @@ run_test    "Renegotiation: gnutls server unsafe, client-inititated legacy" \
             -C "error" \
             -c "HTTP/1.0 200 [Oo][Kk]"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: DTLS, client-initiated" \
             "$P_SRV debug_level=3 dtls=1 exchanges=2 renegotiation=1" \
             "$P_CLI debug_level=3 dtls=1 exchanges=2 renegotiation=1 renegotiate=1" \
@@ -1716,6 +1739,7 @@ run_test    "Renegotiation: DTLS, client-initiated" \
             -s "=> renegotiate" \
             -S "write hello request"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: DTLS, server-initiated" \
             "$P_SRV debug_level=3 dtls=1 exchanges=2 renegotiation=1 renegotiate=1" \
             "$P_CLI debug_level=3 dtls=1 exchanges=2 renegotiation=1 \
@@ -1730,6 +1754,7 @@ run_test    "Renegotiation: DTLS, server-initiated" \
             -s "=> renegotiate" \
             -s "write hello request"
 
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: DTLS, renego_period overflow" \
             "$P_SRV debug_level=3 dtls=1 exchanges=4 renegotiation=1 renego_period=18446462598732840962 auth_mode=optional" \
             "$P_CLI debug_level=3 dtls=1 exchanges=4 renegotiation=1" \
@@ -1741,9 +1766,10 @@ run_test    "Renegotiation: DTLS, renego_period overflow" \
             -s "record counter limit reached: renegotiate" \
             -c "=> renegotiate" \
             -s "=> renegotiate" \
-            -s "write hello request" \
+            -s "write hello request"
 
 requires_gnutls
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "Renegotiation: DTLS, gnutls server, client-initiated" \
             "$G_SRV -u --mtu 4096" \
             "$P_CLI debug_level=3 dtls=1 exchanges=1 renegotiation=1 renegotiate=1" \
@@ -3431,6 +3457,7 @@ run_test    "DTLS reassembly: more fragmentation, nbio (gnutls server)" \
             -C "error"
 
 requires_gnutls
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "DTLS reassembly: fragmentation, renego (gnutls server)" \
             "$G_SRV -u --mtu 256" \
             "$P_CLI debug_level=3 dtls=1 renegotiation=1 renegotiate=1" \
@@ -3444,6 +3471,7 @@ run_test    "DTLS reassembly: fragmentation, renego (gnutls server)" \
             -s "Extra-header:"
 
 requires_gnutls
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "DTLS reassembly: fragmentation, nbio, renego (gnutls server)" \
             "$G_SRV -u --mtu 256" \
             "$P_CLI debug_level=3 nbio=2 dtls=1 renegotiation=1 renegotiate=1" \
@@ -3688,6 +3716,7 @@ run_test    "DTLS proxy: 3d, min handshake, resumption, nbio" \
             -c "HTTP/1.0 200 OK"
 
 needs_more_time 4
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "DTLS proxy: 3d, min handshake, client-initiated renego" \
             -p "$P_PXY drop=5 delay=5 duplicate=5" \
             "$P_SRV dtls=1 hs_timeout=250-10000 tickets=0 auth_mode=none \
@@ -3702,6 +3731,7 @@ run_test    "DTLS proxy: 3d, min handshake, client-initiated renego" \
             -c "HTTP/1.0 200 OK"
 
 needs_more_time 4
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "DTLS proxy: 3d, min handshake, client-initiated renego, nbio" \
             -p "$P_PXY drop=5 delay=5 duplicate=5" \
             "$P_SRV dtls=1 hs_timeout=250-10000 tickets=0 auth_mode=none \
@@ -3716,6 +3746,7 @@ run_test    "DTLS proxy: 3d, min handshake, client-initiated renego, nbio" \
             -c "HTTP/1.0 200 OK"
 
 needs_more_time 4
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "DTLS proxy: 3d, min handshake, server-initiated renego" \
             -p "$P_PXY drop=5 delay=5 duplicate=5" \
             "$P_SRV dtls=1 hs_timeout=250-10000 tickets=0 auth_mode=none \
@@ -3731,6 +3762,7 @@ run_test    "DTLS proxy: 3d, min handshake, server-initiated renego" \
             -c "HTTP/1.0 200 OK"
 
 needs_more_time 4
+requires_config_enabled MBEDTLS_SSL_RENEGOTIATION
 run_test    "DTLS proxy: 3d, min handshake, server-initiated renego, nbio" \
             -p "$P_PXY drop=5 delay=5 duplicate=5" \
             "$P_SRV dtls=1 hs_timeout=250-10000 tickets=0 auth_mode=none \