diff --git a/include/mbedtls/compat-1.3.h b/include/mbedtls/compat-1.3.h
index 600a0f1..213b691 100644
--- a/include/mbedtls/compat-1.3.h
+++ b/include/mbedtls/compat-1.3.h
@@ -1378,7 +1378,8 @@
 #define SSL_ANTI_REPLAY_ENABLED MBEDTLS_SSL_ANTI_REPLAY_ENABLED
 #define SSL_ARC4_DISABLED MBEDTLS_SSL_ARC4_DISABLED
 #define SSL_ARC4_ENABLED MBEDTLS_SSL_ARC4_ENABLED
-#define SSL_BUFFER_LEN MBEDTLS_SSL_BUFFER_LEN
+#define SSL_BUFFER_LEN ( ( ( MBEDTLS_SSL_IN_BUFFER_LEN ) < ( MBEDTLS_SSL_OUT_BUFFER_LEN ) ) \
+                         ? ( MBEDTLS_SSL_IN_BUFFER_LEN ) : ( MBEDTLS_SSL_OUT_BUFFER_LEN ) )
 #define SSL_CACHE_DEFAULT_MAX_ENTRIES MBEDTLS_SSL_CACHE_DEFAULT_MAX_ENTRIES
 #define SSL_CACHE_DEFAULT_TIMEOUT MBEDTLS_SSL_CACHE_DEFAULT_TIMEOUT
 #define SSL_CBC_RECORD_SPLITTING_DISABLED MBEDTLS_SSL_CBC_RECORD_SPLITTING_DISABLED
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 307b90b..667177a 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -2896,7 +2896,51 @@
 //#define MBEDTLS_SSL_CACHE_DEFAULT_MAX_ENTRIES      50 /**< Maximum entries in cache */
 
 /* SSL options */
-//#define MBEDTLS_SSL_MAX_CONTENT_LEN             16384 /**< Maxium fragment length in bytes, determines the size of each of the two internal I/O buffers */
+
+/** \def MBEDTLS_SSL_MAX_CONTENT_LEN
+ *
+ * Maximum fragment length in bytes.
+ *
+ * Determines the size of both the incoming and outgoing TLS I/O buffers.
+ *
+ * Uncommenting MBEDTLS_SSL_IN_CONTENT_LEN and/or MBEDTLS_SSL_OUT_CONTENT_LEN
+ * will override this length by setting maximum incoming and/or outgoing
+ * fragment length, respectively.
+ */
+//#define MBEDTLS_SSL_MAX_CONTENT_LEN             16384
+
+/** \def MBEDTLS_SSL_IN_CONTENT_LEN
+ *
+ * Maximum incoming fragment length in bytes.
+ *
+ * Uncomment to set the size of the inward TLS buffer independently of the
+ * outward buffer.
+ */
+//#define MBEDTLS_SSL_IN_CONTENT_LEN              16384
+
+/** \def MBEDTLS_SSL_OUT_CONTENT_LEN
+ *
+ * Maximum outgoing fragment length in bytes.
+ *
+ * Uncomment to set the size of the outward TLS buffer independently of the
+ * inward buffer.
+ *
+ * It is possible to save RAM by setting a smaller outward buffer, while keeping
+ * the default inward 16384 byte buffer to conform to the TLS specification.
+ *
+ * The minimum required outward buffer size is determined by the handshake
+ * protocol's usage. Handshaking will fail if the outward buffer is too small.
+ * The specific size requirement depends on the configured ciphers and any
+ * certificate data which is sent during the handshake.
+ *
+ * For absolute minimum RAM usage, it's best to enable
+ * MBEDTLS_SSL_MAX_FRAGMENT_LENGTH and reduce MBEDTLS_SSL_MAX_CONTENT_LEN. This
+ * reduces both incoming and outgoing buffer sizes. However this is only
+ * guaranteed if the other end of the connection also supports the TLS
+ * max_fragment_len extension. Otherwise the connection may fail.
+ */
+//#define MBEDTLS_SSL_OUT_CONTENT_LEN             16384
+
 //#define MBEDTLS_SSL_DEFAULT_TICKET_LIFETIME     86400 /**< Lifetime of session tickets (if enabled) */
 //#define MBEDTLS_PSK_MAX_LEN               32 /**< Max size of TLS pre-shared keys, in bytes (default 256 bits) */
 //#define MBEDTLS_SSL_COOKIE_TIMEOUT        60 /**< Default expiration delay of DTLS cookies, in seconds if HAVE_TIME, or in number of cookies issued */
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 4513550..886c14c 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -220,7 +220,7 @@
 #endif
 
 /*
- * Maxium fragment length in bytes,
+ * Maximum fragment length in bytes,
  * determines the size of each of the two internal I/O buffers.
  *
  * Note: the RFC defines the default size of SSL / TLS messages. If you
@@ -234,6 +234,14 @@
 #define MBEDTLS_SSL_MAX_CONTENT_LEN         16384   /**< Size of the input / output buffer */
 #endif
 
+#if !defined(MBEDTLS_SSL_IN_CONTENT_LEN)
+#define MBEDTLS_SSL_IN_CONTENT_LEN MBEDTLS_SSL_MAX_CONTENT_LEN
+#endif
+
+#if !defined(MBEDTLS_SSL_OUT_CONTENT_LEN)
+#define MBEDTLS_SSL_OUT_CONTENT_LEN MBEDTLS_SSL_MAX_CONTENT_LEN
+#endif
+
 /* \} name SECTION: Module settings */
 
 /*
@@ -2418,7 +2426,8 @@
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
 /**
  * \brief          Set the maximum fragment length to emit and/or negotiate
- *                 (Default: MBEDTLS_SSL_MAX_CONTENT_LEN, usually 2^14 bytes)
+ *                 (Default: the smaller of MBEDTLS_SSL_IN_CONTENT_LEN and
+ *                 MBEDTLS_SSL_OUT_CONTENT_LEN, usually 2^14 bytes)
  *                 (Server: set maximum fragment length to emit,
  *                 usually negotiated by the client during handshake
  *                 (Client: set maximum fragment length to emit *and*
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index f48fe90..d214703 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -143,32 +143,73 @@
 #define MBEDTLS_SSL_PADDING_ADD              0
 #endif
 
-#define MBEDTLS_SSL_PAYLOAD_LEN ( MBEDTLS_SSL_MAX_CONTENT_LEN    \
-                        + MBEDTLS_SSL_COMPRESSION_ADD            \
-                        + MBEDTLS_MAX_IV_LENGTH                  \
-                        + MBEDTLS_SSL_MAC_ADD                    \
-                        + MBEDTLS_SSL_PADDING_ADD                \
-                        )
+#define MBEDTLS_SSL_PAYLOAD_OVERHEAD ( MBEDTLS_SSL_COMPRESSION_ADD +    \
+                                       MBEDTLS_MAX_IV_LENGTH +          \
+                                       MBEDTLS_SSL_MAC_ADD +            \
+                                       MBEDTLS_SSL_PADDING_ADD          \
+                                       )
+
+#define MBEDTLS_SSL_IN_PAYLOAD_LEN ( MBEDTLS_SSL_PAYLOAD_OVERHEAD + \
+                                     ( MBEDTLS_SSL_IN_CONTENT_LEN ) )
+
+#define MBEDTLS_SSL_OUT_PAYLOAD_LEN ( MBEDTLS_SSL_PAYLOAD_OVERHEAD + \
+                                      ( MBEDTLS_SSL_OUT_CONTENT_LEN ) )
+
+/* Maximum length we can advertise as our max content length for
+   RFC 6066 max_fragment_length extension negotiation purposes
+   (the lesser of both sizes, if they are unequal.)
+ */
+#define MBEDTLS_TLS_EXT_ADV_CONTENT_LEN (                            \
+        (MBEDTLS_SSL_IN_CONTENT_LEN > MBEDTLS_SSL_OUT_CONTENT_LEN)   \
+        ? ( MBEDTLS_SSL_OUT_CONTENT_LEN )                            \
+        : ( MBEDTLS_SSL_IN_CONTENT_LEN )                             \
+        )
 
 /*
  * Check that we obey the standard's message size bounds
  */
 
 #if MBEDTLS_SSL_MAX_CONTENT_LEN > 16384
-#error Bad configuration - record content too large.
+#error "Bad configuration - record content too large."
 #endif
 
-#if MBEDTLS_SSL_PAYLOAD_LEN > 16384 + 2048
-#error Bad configuration - protected record payload too large.
+#if MBEDTLS_SSL_IN_CONTENT_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN
+#error "Bad configuration - incoming record content should not be larger than MBEDTLS_SSL_MAX_CONTENT_LEN."
 #endif
 
+#if MBEDTLS_SSL_OUT_CONTENT_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN
+#error "Bad configuration - outgoing record content should not be larger than MBEDTLS_SSL_MAX_CONTENT_LEN."
+#endif
+
+#if MBEDTLS_SSL_IN_PAYLOAD_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN + 2048
+#error "Bad configuration - incoming protected record payload too large."
+#endif
+
+#if MBEDTLS_SSL_OUT_PAYLOAD_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN + 2048
+#error "Bad configuration - outgoing protected record payload too large."
+#endif
+
+/* Calculate buffer sizes */
+
 /* Note: Even though the TLS record header is only 5 bytes
    long, we're internally using 8 bytes to store the
    implicit sequence number. */
 #define MBEDTLS_SSL_HEADER_LEN 13
 
-#define MBEDTLS_SSL_BUFFER_LEN  \
-    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_PAYLOAD_LEN ) )
+#define MBEDTLS_SSL_IN_BUFFER_LEN  \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_IN_PAYLOAD_LEN ) )
+
+#define MBEDTLS_SSL_OUT_BUFFER_LEN  \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_OUT_PAYLOAD_LEN ) )
+
+#ifdef MBEDTLS_ZLIB_SUPPORT
+/* Compression buffer holds both IN and OUT buffers, so should be size of the larger */
+#define MBEDTLS_SSL_COMPRESS_BUFFER_LEN (                               \
+        ( MBEDTLS_SSL_IN_BUFFER_LEN > MBEDTLS_SSL_OUT_BUFFER_LEN )      \
+        ? MBEDTLS_SSL_IN_BUFFER_LEN                                     \
+        : MBEDTLS_SSL_OUT_BUFFER_LEN                                    \
+        )
+#endif
 
 /*
  * TLS extension flags (for extensions with outgoing ServerHello content