Index: src/OFTCPSocket.h
==================================================================
--- src/OFTCPSocket.h
+++ src/OFTCPSocket.h
@@ -87,11 +87,12 @@
 	OFString *_Nullable _SOCKS5Host;
 	uint16_t _SOCKS5Port;
 #ifdef OF_WII
 	uint16_t _port;
 #endif
-	OF_RESERVE_IVARS(OFTCPSocket, 4)
+	uintptr_t _usesMPTCP;	/* Change to bool on ABI bump */
+	OF_RESERVE_IVARS(OFTCPSocket, 3)
 }
 
 #ifdef OF_HAVE_CLASS_PROPERTIES
 @property (class, nullable, copy, nonatomic) OFString *SOCKS5Host;
 @property (class, nonatomic) uint16_t SOCKS5Port;
@@ -120,10 +121,18 @@
  * @throw OFSetOptionFailedException The option could not be set
  */
 @property (nonatomic) bool canDelaySendingSegments;
 #endif
 
+/**
+ * @brief Whether the socket uses MPTCP.
+ *
+ * If you want to use MPTCP, set this to true before connecting or binding.
+ * After connecting or binding, this returns whether MPTCP was used.
+ */
+@property (nonatomic) bool usesMPTCP;
+
 /**
  * @brief The host to use as a SOCKS5 proxy.
  */
 @property OF_NULLABLE_PROPERTY (copy, nonatomic) OFString *SOCKS5Host;
 

Index: src/OFTCPSocket.m
==================================================================
--- src/OFTCPSocket.m
+++ src/OFTCPSocket.m
@@ -50,10 +50,14 @@
 #import "OFBindIPSocketFailedException.h"
 #import "OFGetOptionFailedException.h"
 #import "OFNotImplementedException.h"
 #import "OFNotOpenException.h"
 #import "OFSetOptionFailedException.h"
+
+#ifdef OF_LINUX
+# include <linux/mptcp.h>
+#endif
 
 static const OFRunLoopMode connectRunLoopMode =
     @"OFTCPSocketConnectRunLoopMode";
 
 static OFString *defaultSOCKS5Host = nil;
@@ -141,19 +145,36 @@
 {
 #if SOCK_CLOEXEC == 0 && defined(HAVE_FCNTL) && defined(FD_CLOEXEC)
 	int flags;
 #endif
 
-	if (_socket != OFInvalidSocketHandle)
+	if (_socket != OFInvalidSocketHandle) {
 		@throw [OFAlreadyOpenException exceptionWithObject: self];
-
-	if ((_socket = socket(
-	    ((struct sockaddr *)&address->sockaddr)->sa_family,
-	    SOCK_STREAM | SOCK_CLOEXEC, 0)) == OFInvalidSocketHandle) {
-		*errNo = _OFSocketErrNo();
-		return false;
 	}
+
+#ifdef OF_LINUX
+	if (_usesMPTCP) {
+		if ((_socket = socket(
+		    ((struct sockaddr *)&address->sockaddr)->sa_family,
+		    SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_MPTCP)) ==
+		    OFInvalidSocketHandle) {
+			if ((_socket = socket(
+			    ((struct sockaddr *)&address->sockaddr)->sa_family,
+			    SOCK_STREAM | SOCK_CLOEXEC, 0)) ==
+			    OFInvalidSocketHandle) {
+				*errNo = _OFSocketErrNo();
+				return false;
+			}
+		}
+	} else
+#endif
+		if ((_socket = socket(
+		    ((struct sockaddr *)&address->sockaddr)->sa_family,
+		    SOCK_STREAM | SOCK_CLOEXEC, 0)) == OFInvalidSocketHandle) {
+			*errNo = _OFSocketErrNo();
+			return false;
+		}
 
 #if SOCK_CLOEXEC == 0 && defined(HAVE_FCNTL) && defined(FD_CLOEXEC)
 	if ((flags = fcntl(_socket, F_GETFD, 0)) != -1)
 		fcntl(_socket, F_SETFD, flags | FD_CLOEXEC);
 #endif
@@ -346,18 +367,36 @@
 		      addressFamily: OFSocketAddressFamilyAny];
 
 	address = *(OFSocketAddress *)[socketAddresses itemAtIndex: 0];
 	OFSocketAddressSetIPPort(&address, port);
 
-	if ((_socket = socket(
-	    ((struct sockaddr *)&address.sockaddr)->sa_family,
-	    SOCK_STREAM | SOCK_CLOEXEC, 0)) == OFInvalidSocketHandle)
-		@throw [OFBindIPSocketFailedException
-		    exceptionWithHost: host
-				 port: port
-			       socket: self
-				errNo: _OFSocketErrNo()];
+#ifdef OF_LINUX
+	if (_usesMPTCP) {
+		if ((_socket = socket(
+		    ((struct sockaddr *)&address.sockaddr)->sa_family,
+		    SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_MPTCP)) ==
+		    OFInvalidSocketHandle) {
+			if ((_socket = socket(
+			    ((struct sockaddr *)&address.sockaddr)->sa_family,
+			    SOCK_STREAM | SOCK_CLOEXEC, 0)) ==
+			    OFInvalidSocketHandle)
+				@throw [OFBindIPSocketFailedException
+				    exceptionWithHost: host
+						 port: port
+					       socket: self
+						errNo: _OFSocketErrNo()];
+		}
+	} else
+#endif
+		if ((_socket = socket(
+		    ((struct sockaddr *)&address.sockaddr)->sa_family,
+		    SOCK_STREAM | SOCK_CLOEXEC, 0)) == OFInvalidSocketHandle)
+			@throw [OFBindIPSocketFailedException
+			    exceptionWithHost: host
+					 port: port
+				       socket: self
+					errNo: _OFSocketErrNo()];
 
 	_canBlock = true;
 
 #if SOCK_CLOEXEC == 0 && defined(HAVE_FCNTL) && defined(FD_CLOEXEC)
 	if ((flags = fcntl(_socket, F_GETFD, 0)) != -1)
@@ -509,10 +548,28 @@
 				  errNo: _OFSocketErrNo()];
 
 	return !v;
 }
 #endif
+
+- (void)setUsesMPTCP: (bool)usesMPTCP
+{
+	_usesMPTCP = usesMPTCP;
+}
+
+- (bool)usesMPTCP
+{
+#ifdef OF_LINUX
+	struct mptcp_info info;
+	socklen_t infoLen = (socklen_t)sizeof(info);
+
+	if (getsockopt(_socket, SOL_MPTCP, MPTCP_INFO, &info, &infoLen) != -1)
+		return true;
+#endif
+
+	return false;
+}
 
 - (void)close
 {
 #ifdef OF_WII
 	_port = 0;