diff --git a/lib/client/CClient.cpp b/lib/client/CClient.cpp
index f1f4ae22..59bbc4fc 100644
--- a/lib/client/CClient.cpp
+++ b/lib/client/CClient.cpp
@@ -257,6 +257,12 @@ CClient::mouseMove(SInt32 x, SInt32 y)
 	m_screen->mouseMove(x, y);
 }
 
+void
+CClient::mouseRelativeMove(SInt32 dx, SInt32 dy)
+{
+	m_screen->mouseRelativeMove(dx, dy);
+}
+
 void
 CClient::mouseWheel(SInt32 delta)
 {
diff --git a/lib/client/CClient.h b/lib/client/CClient.h
index 9c49d3cd..5087759b 100644
--- a/lib/client/CClient.h
+++ b/lib/client/CClient.h
@@ -135,6 +135,7 @@ public:
 	virtual void		mouseDown(ButtonID);
 	virtual void		mouseUp(ButtonID);
 	virtual void		mouseMove(SInt32 xAbs, SInt32 yAbs);
+	virtual void		mouseRelativeMove(SInt32 xRel, SInt32 yRel);
 	virtual void		mouseWheel(SInt32 delta);
 	virtual void		screensaver(bool activate);
 	virtual void		resetOptions();
diff --git a/lib/platform/CXWindowsScreen.cpp b/lib/platform/CXWindowsScreen.cpp
index ffe5a64e..7aee2341 100644
--- a/lib/platform/CXWindowsScreen.cpp
+++ b/lib/platform/CXWindowsScreen.cpp
@@ -550,6 +550,19 @@ CXWindowsScreen::fakeMouseMove(SInt32 x, SInt32 y) const
 	XFlush(m_display);
 }
 
+void
+CXWindowsScreen::fakeMouseRelativeMove(SInt32 dx, SInt32 dy) const
+{
+	// FIXME -- ignore xinerama for now
+	if (false && m_xinerama && m_xtestIsXineramaUnaware) {
+//		XWarpPointer(m_display, None, m_root, 0, 0, 0, 0, x, y);
+	}
+	else {
+		XTestFakeRelativeMotionEvent(m_display, dx, dy, CurrentTime);
+	}
+	XFlush(m_display);
+}
+
 void
 CXWindowsScreen::fakeMouseWheel(SInt32 delta) const
 {
diff --git a/lib/platform/CXWindowsScreen.h b/lib/platform/CXWindowsScreen.h
index c7be5bb4..d1289dca 100644
--- a/lib/platform/CXWindowsScreen.h
+++ b/lib/platform/CXWindowsScreen.h
@@ -55,6 +55,7 @@ public:
 	// ISecondaryScreen overrides
 	virtual void		fakeMouseButton(ButtonID id, bool press) const;
 	virtual void		fakeMouseMove(SInt32 x, SInt32 y) const;
+	virtual void		fakeMouseRelativeMove(SInt32 dx, SInt32 dy) const;
 	virtual void		fakeMouseWheel(SInt32 delta) const;
 
 	// IPlatformScreen overrides
diff --git a/lib/server/CClientProxy.h b/lib/server/CClientProxy.h
index 9453a203..b8e38fa8 100644
--- a/lib/server/CClientProxy.h
+++ b/lib/server/CClientProxy.h
@@ -96,6 +96,7 @@ public:
 	virtual void		mouseDown(ButtonID) = 0;
 	virtual void		mouseUp(ButtonID) = 0;
 	virtual void		mouseMove(SInt32 xAbs, SInt32 yAbs) = 0;
+	virtual void		mouseRelativeMove(SInt32 xRel, SInt32 yRel) = 0;
 	virtual void		mouseWheel(SInt32 delta) = 0;
 	virtual void		screensaver(bool activate) = 0;
 	virtual void		resetOptions() = 0;
diff --git a/lib/server/CClientProxy1_0.cpp b/lib/server/CClientProxy1_0.cpp
index 617e12a2..2bb412ce 100644
--- a/lib/server/CClientProxy1_0.cpp
+++ b/lib/server/CClientProxy1_0.cpp
@@ -316,6 +316,12 @@ CClientProxy1_0::mouseMove(SInt32 xAbs, SInt32 yAbs)
 	CProtocolUtil::writef(getStream(), kMsgDMouseMove, xAbs, yAbs);
 }
 
+void
+CClientProxy1_0::mouseRelativeMove(SInt32, SInt32)
+{
+	// ignore -- not supported in protocol 1.0
+}
+
 void
 CClientProxy1_0::mouseWheel(SInt32 delta)
 {
diff --git a/lib/server/CClientProxy1_0.h b/lib/server/CClientProxy1_0.h
index 503dcba9..4f752085 100644
--- a/lib/server/CClientProxy1_0.h
+++ b/lib/server/CClientProxy1_0.h
@@ -49,6 +49,7 @@ public:
 	virtual void		mouseDown(ButtonID);
 	virtual void		mouseUp(ButtonID);
 	virtual void		mouseMove(SInt32 xAbs, SInt32 yAbs);
+	virtual void		mouseRelativeMove(SInt32 xRel, SInt32 yRel);
 	virtual void		mouseWheel(SInt32 delta);
 	virtual void		screensaver(bool activate);
 	virtual void		resetOptions();
diff --git a/lib/server/CClientProxyUnknown.cpp b/lib/server/CClientProxyUnknown.cpp
index 4c45ba07..806f23b8 100644
--- a/lib/server/CClientProxyUnknown.cpp
+++ b/lib/server/CClientProxyUnknown.cpp
@@ -15,6 +15,7 @@
 #include "CClientProxyUnknown.h"
 #include "CClientProxy1_0.h"
 #include "CClientProxy1_1.h"
+#include "CClientProxy1_2.h"
 #include "ProtocolTypes.h"
 #include "CProtocolUtil.h"
 #include "XSynergy.h"
@@ -214,6 +215,10 @@ CClientProxyUnknown::handleData(const CEvent&, void*)
 			case 1:
 				m_proxy = new CClientProxy1_1(name, m_stream);
 				break;
+
+			case 2:
+				m_proxy = new CClientProxy1_2(name, m_stream);
+				break;
 			}
 		}
 
diff --git a/lib/server/CConfig.cpp b/lib/server/CConfig.cpp
index a4893cc8..03e0eb2d 100644
--- a/lib/server/CConfig.cpp
+++ b/lib/server/CConfig.cpp
@@ -629,6 +629,9 @@ CConfig::getOptionName(OptionID id)
 	if (id == kOptionXTestXineramaUnaware) {
 		return "xtestIsXineramaUnaware";
 	}
+	if (id == kOptionRelativeMouseMoves) {
+		return "relativeMouseMoves";
+	}
 	return NULL;
 }
 
@@ -638,7 +641,8 @@ CConfig::getOptionValue(OptionID id, OptionValue value)
 	if (id == kOptionHalfDuplexCapsLock ||
 		id == kOptionHalfDuplexNumLock ||
 		id == kOptionScreenSaverSync ||
-		id == kOptionXTestXineramaUnaware) {
+		id == kOptionXTestXineramaUnaware ||
+		id == kOptionRelativeMouseMoves) {
 		return (value != 0) ? "true" : "false";
 	}
 	if (id == kOptionModifierMapForShift ||
@@ -778,6 +782,9 @@ CConfig::readSectionOptions(std::istream& s)
 		else if (name == "screenSaverSync") {
 			addOption("", kOptionScreenSaverSync, parseBoolean(value));
 		}
+		else if (name == "relativeMouseMoves") {
+			addOption("", kOptionRelativeMouseMoves, parseBoolean(value));
+		}
 		else {
 			throw XConfigRead("unknown argument");
 		}
diff --git a/lib/server/CPrimaryClient.cpp b/lib/server/CPrimaryClient.cpp
index a8e21c3c..7ec681bc 100644
--- a/lib/server/CPrimaryClient.cpp
+++ b/lib/server/CPrimaryClient.cpp
@@ -185,6 +185,12 @@ CPrimaryClient::mouseMove(SInt32 x, SInt32 y)
 	m_screen->warpCursor(x, y);
 }
 
+void
+CPrimaryClient::mouseRelativeMove(SInt32, SInt32)
+{
+	// ignore
+}
+
 void
 CPrimaryClient::mouseWheel(SInt32)
 {
diff --git a/lib/server/CPrimaryClient.h b/lib/server/CPrimaryClient.h
index 985fc4a3..2006508c 100644
--- a/lib/server/CPrimaryClient.h
+++ b/lib/server/CPrimaryClient.h
@@ -102,6 +102,7 @@ public:
 	virtual void		mouseDown(ButtonID);
 	virtual void		mouseUp(ButtonID);
 	virtual void		mouseMove(SInt32 xAbs, SInt32 yAbs);
+	virtual void		mouseRelativeMove(SInt32 xRel, SInt32 yRel);
 	virtual void		mouseWheel(SInt32 delta);
 	virtual void		screensaver(bool activate);
 	virtual void		resetOptions();
diff --git a/lib/server/CServer.cpp b/lib/server/CServer.cpp
index 27a8651a..fce2584a 100644
--- a/lib/server/CServer.cpp
+++ b/lib/server/CServer.cpp
@@ -53,7 +53,8 @@ CServer::CServer(const CConfig& config, CPrimaryClient* primaryClient) :
 	m_switchTwoTapDelay(0.0),
 	m_switchTwoTapEngaged(false),
 	m_switchTwoTapArmed(false),
-	m_switchTwoTapZone(3)
+	m_switchTwoTapZone(3),
+	m_relativeMoves(false)
 {
 	// must have a primary client and it must have a canonical name
 	assert(m_primaryClient != NULL);
@@ -283,6 +284,9 @@ CServer::onCommandKey(KeyID id, KeyModifierMask /*mask*/, bool /*down*/)
 {
 	if (id == kKeyScrollLock) {
 		m_primaryClient->reconfigure(getActivePrimarySides());
+		if (!isLockedToScreenServer()) {
+			stopRelativeMoves();
+		}
 	}
 	return false;
 }
@@ -322,13 +326,7 @@ bool
 CServer::isLockedToScreenServer() const
 {
 	// locked if scroll-lock is toggled on
-	if ((m_primaryClient->getToggleMask() & KeyModifierScrollLock) != 0) {
-		LOG((CLOG_DEBUG "locked by ScrollLock"));
-		return true;
-	}
-
-	// not locked
-	return false;
+	return ((m_primaryClient->getToggleMask() & KeyModifierScrollLock) != 0);
 }
 
 bool
@@ -336,6 +334,7 @@ CServer::isLockedToScreen() const
 {
 	// locked if we say we're locked
 	if (isLockedToScreenServer()) {
+		LOG((CLOG_DEBUG "locked by ScrollLock"));
 		return true;
 	}
 
@@ -841,6 +840,24 @@ CServer::isSwitchWaitStarted() const
 	return (m_switchWaitTimer != NULL);
 }
 
+void
+CServer::stopRelativeMoves()
+{
+	if (m_relativeMoves && m_active != m_primaryClient) {
+		// warp to the center of the active client so we know where we are
+		SInt32 ax, ay, aw, ah;
+		m_active->getShape(ax, ay, aw, ah);
+		m_x       = ax + (aw >> 1);
+		m_y       = ay + (ah >> 1);
+		m_xDelta  = 0;
+		m_yDelta  = 0;
+		m_xDelta2 = 0;
+		m_yDelta2 = 0;
+		LOG((CLOG_DEBUG2 "synchronize move on %s by %d,%d", getName(m_active).c_str(), m_x, m_y));
+		m_active->mouseMove(m_x, m_y);
+	}
+}
+
 void
 CServer::sendOptions(IClient* client) const
 {
@@ -883,6 +900,7 @@ CServer::processOptions()
 		return;
 	}
 
+	bool newRelativeMoves = m_relativeMoves;
 	for (CConfig::CScreenOptions::const_iterator index = options->begin();
 								index != options->end(); ++index) {
 		const OptionID id       = index->first;
@@ -901,7 +919,15 @@ CServer::processOptions()
 			}
 			stopSwitchTwoTap();
 		}
+		else if (id == kOptionRelativeMouseMoves) {
+			newRelativeMoves = (value != 0);
+		}
 	}
+
+	if (m_relativeMoves && !newRelativeMoves) {
+		stopRelativeMoves();
+	}
+	m_relativeMoves = newRelativeMoves;
 }
 
 void
@@ -1339,6 +1365,18 @@ CServer::onMouseMoveSecondary(SInt32 dx, SInt32 dy)
 		return;
 	}
 
+	// if doing relative motion on secondary screens and we're locked
+	// to the screen (which activates relative moves) then send a
+	// relative mouse motion.  when we're doing this we pretend as if
+	// the mouse isn't actually moving because we're expecting some
+	// program on the secondary screen to warp the mouse on us, so we
+	// have no idea where it really is.
+	if (m_relativeMoves && isLockedToScreenServer()) {
+		LOG((CLOG_DEBUG2 "relative move on %s by %d,%d", getName(m_active).c_str(), dx, dy));
+		m_active->mouseRelativeMove(dx, dy);
+		return;
+	}
+
 	// save old position
 	const SInt32 xOld = m_x;
 	const SInt32 yOld = m_y;
diff --git a/lib/server/CServer.h b/lib/server/CServer.h
index 0e28eee7..3272d837 100644
--- a/lib/server/CServer.h
+++ b/lib/server/CServer.h
@@ -26,8 +26,6 @@
 #include "stdset.h"
 #include "stdvector.h"
 
-class CClientProxy;
-class CClientProxyUnknown;
 class CEventQueueTimer;
 class CPrimaryClient;
 class IClient;
@@ -183,6 +181,9 @@ private:
 	// returns true iff the delay switch timer is started
 	bool				isSwitchWaitStarted() const;
 
+	// stop relative mouse moves
+	void				stopRelativeMoves();
+
 	// send screen options to \c client
 	void				sendOptions(IClient* client) const;
 
@@ -312,6 +313,9 @@ private:
 	bool				m_switchTwoTapArmed;
 	SInt32				m_switchTwoTapZone;
 
+	// relative mouse move option
+	bool				m_relativeMoves;
+
 	static CEvent::Type	s_errorEvent;
 	static CEvent::Type	s_disconnectedEvent;
 };
diff --git a/lib/server/Makefile.am b/lib/server/Makefile.am
index 7ffb76b4..90f3d6e1 100644
--- a/lib/server/Makefile.am
+++ b/lib/server/Makefile.am
@@ -27,6 +27,7 @@ libserver_a_SOURCES = 				\
 	CClientProxy.cpp				\
 	CClientProxy1_0.cpp				\
 	CClientProxy1_1.cpp				\
+	CClientProxy1_2.cpp				\
 	CClientProxyUnknown.cpp			\
 	CConfig.cpp						\
 	CPrimaryClient.cpp				\
@@ -35,6 +36,7 @@ libserver_a_SOURCES = 				\
 	CClientProxy.h					\
 	CClientProxy1_0.h				\
 	CClientProxy1_1.h				\
+	CClientProxy1_2.h				\
 	CClientProxyUnknown.h			\
 	CConfig.h						\
 	CPrimaryClient.h				\
diff --git a/lib/synergy/CPlatformScreen.h b/lib/synergy/CPlatformScreen.h
index b5fcde01..d5bb7fbb 100644
--- a/lib/synergy/CPlatformScreen.h
+++ b/lib/synergy/CPlatformScreen.h
@@ -45,6 +45,7 @@ public:
 	// ISecondaryScreen overrides
 	virtual void		fakeMouseButton(ButtonID id, bool press) const = 0;
 	virtual void		fakeMouseMove(SInt32 x, SInt32 y) const = 0;
+	virtual void		fakeMouseRelativeMove(SInt32 dx, SInt32 dy) const = 0;
 	virtual void		fakeMouseWheel(SInt32 delta) const = 0;
 
 	// IKeyState overrides
diff --git a/lib/synergy/CScreen.cpp b/lib/synergy/CScreen.cpp
index 787e72ba..67140498 100644
--- a/lib/synergy/CScreen.cpp
+++ b/lib/synergy/CScreen.cpp
@@ -222,6 +222,13 @@ CScreen::mouseMove(SInt32 x, SInt32 y)
 	m_screen->fakeMouseMove(x, y);
 }
 
+void
+CScreen::mouseRelativeMove(SInt32 dx, SInt32 dy)
+{
+	assert(!m_isPrimary);
+	m_screen->fakeMouseRelativeMove(dx, dy);
+}
+
 void
 CScreen::mouseWheel(SInt32 delta)
 {
diff --git a/lib/synergy/CScreen.h b/lib/synergy/CScreen.h
index ae605d9b..01b10417 100644
--- a/lib/synergy/CScreen.h
+++ b/lib/synergy/CScreen.h
@@ -146,6 +146,13 @@ public:
 	*/
 	void				mouseMove(SInt32 xAbs, SInt32 yAbs);
 
+	//! Notify of mouse motion
+	/*!
+	Synthesize mouse events to generate mouse motion by the relative
+	amount \c xRel,yRel.
+	*/
+	void				mouseRelativeMove(SInt32 xRel, SInt32 yRel);
+
 	//! Notify of mouse wheel motion
 	/*!
 	Synthesize mouse events to generate mouse wheel motion of \c delta.
diff --git a/lib/synergy/IClient.h b/lib/synergy/IClient.h
index b4ef2eca..7679d104 100644
--- a/lib/synergy/IClient.h
+++ b/lib/synergy/IClient.h
@@ -120,6 +120,13 @@ public:
 	*/
 	virtual void		mouseMove(SInt32 xAbs, SInt32 yAbs) = 0;
 
+	//! Notify of mouse motion
+	/*!
+	Synthesize mouse events to generate mouse motion by the relative
+	amount \c xRel,yRel.
+	*/
+	virtual void		mouseRelativeMove(SInt32 xRel, SInt32 yRel) = 0;
+
 	//! Notify of mouse wheel motion
 	/*!
 	Synthesize mouse events to generate mouse wheel motion of \c delta.
diff --git a/lib/synergy/IPlatformScreen.h b/lib/synergy/IPlatformScreen.h
index 13bd0a31..8a5da677 100644
--- a/lib/synergy/IPlatformScreen.h
+++ b/lib/synergy/IPlatformScreen.h
@@ -153,6 +153,7 @@ public:
 	// ISecondaryScreen overrides
 	virtual void		fakeMouseButton(ButtonID id, bool press) const = 0;
 	virtual void		fakeMouseMove(SInt32 x, SInt32 y) const = 0;
+	virtual void		fakeMouseRelativeMove(SInt32 dx, SInt32 dy) const = 0;
 	virtual void		fakeMouseWheel(SInt32 delta) const = 0;
 
 	// IKeyState overrides
diff --git a/lib/synergy/ISecondaryScreen.h b/lib/synergy/ISecondaryScreen.h
index 1311e7af..092cd805 100644
--- a/lib/synergy/ISecondaryScreen.h
+++ b/lib/synergy/ISecondaryScreen.h
@@ -40,6 +40,12 @@ public:
 	*/
 	virtual void		fakeMouseMove(SInt32 x, SInt32 y) const = 0;
 
+	//! Fake mouse move
+	/*!
+	Synthesize a mouse move to the relative coordinates \c dx,dy.
+	*/
+	virtual void		fakeMouseRelativeMove(SInt32 dx, SInt32 dy) const = 0;
+
 	//! Fake mouse wheel
 	/*!
 	Synthesize a mouse wheel event of amount \c delta.
diff --git a/lib/synergy/OptionTypes.h b/lib/synergy/OptionTypes.h
index aaefe7fa..31504993 100644
--- a/lib/synergy/OptionTypes.h
+++ b/lib/synergy/OptionTypes.h
@@ -55,6 +55,7 @@ static const OptionID	kOptionScreenSwitchDelay     = OPTION_CODE("SSWT");
 static const OptionID	kOptionScreenSwitchTwoTap    = OPTION_CODE("SSTT");
 static const OptionID	kOptionScreenSaverSync       = OPTION_CODE("SSVR");
 static const OptionID	kOptionXTestXineramaUnaware  = OPTION_CODE("XTXU");
+static const OptionID	kOptionRelativeMouseMoves    = OPTION_CODE("MDLT");
 //@}
 
 #undef OPTION_CODE
diff --git a/lib/synergy/ProtocolTypes.h b/lib/synergy/ProtocolTypes.h
index c1162c2d..4fd6d475 100644
--- a/lib/synergy/ProtocolTypes.h
+++ b/lib/synergy/ProtocolTypes.h
@@ -21,7 +21,7 @@
 // 1.0:  initial protocol
 // 1.1:  adds KeyCode to key press, release, and repeat
 static const SInt16		kProtocolMajorVersion = 1;
-static const SInt16		kProtocolMinorVersion = 1;
+static const SInt16		kProtocolMinorVersion = 2;
 
 // default contact port number
 static const UInt16		kDefaultPort = 24800;
@@ -180,6 +180,10 @@ static const char		kMsgDMouseUp[]		= "DMUP%1i";
 // $1 = x, $2 = y.  x,y are absolute screen coordinates.
 static const char		kMsgDMouseMove[]	= "DMMV%2i%2i";
 
+// relative mouse move:  primary -> secondary
+// $1 = dx, $2 = dy.  dx,dy are motion deltas.
+static const char		kMsgDMouseRelMove[]	= "DMRM%2i%2i";
+
 // mouse button pressed:  primary -> secondary
 // $1 = delta.  the delta should be +120 for one tick forward (away
 // from the user) and -120 for one tick backward (toward the user).