diff --git a/configure.in b/configure.in
index a066a4d1..884b3481 100644
--- a/configure.in
+++ b/configure.in
@@ -104,23 +104,27 @@ if test x"$acx_host_winapi" = xXWINDOWS; then
 		[$X_LIBS -lXext -lX11 $X_EXTRA_LIBS])
 	AC_CHECK_HEADERS([X11/extensions/XTest.h],,
 		AC_MSG_ERROR(You must have the XTest headers to compile synergy))
-	AC_CHECK_LIB(Xinerama,
-		XineramaQueryExtension,
-		[X_LIBS="$X_LIBS -lXinerama"],
+	AC_CHECK_HEADERS([X11/extensions/Xinerama.h],
+		[acx_xinerama_lib_ok=yes],
 		[acx_xinerama_lib_ok=no],
-		[$X_LIBS -lXext -lX11 $X_EXTRA_LIBS])
-	if test x"$acx_xinerama_lib_ok" != xno; then
-		AC_CHECK_HEADERS([X11/extensions/Xinerama.h],,,
-			[#include <X11/Xlib.h>])
+		[#include <X11/Xlib.h>])
+	if test x"$acx_xinerama_lib_ok" = xyes; then
+		AC_CHECK_LIB(Xinerama,
+			XineramaQueryExtension,
+			[X_LIBS="$X_LIBS -lXinerama"],
+			[AC_DEFINE(HAVE_X11_EXTENSIONS_XINERAMA_H, 0)],
+			[$X_LIBS -lXext -lX11 $X_EXTRA_LIBS])
 	fi
-	AC_CHECK_LIB(Xext,
-		DPMSQueryExtension,
+	AC_CHECK_HEADERS([X11/extensions/dpms.h],
 		[acx_dpms_lib_ok=yes],
 		[acx_dpms_lib_ok=no],
-		[$X_LIBS -lX11 $X_EXTRA_LIBS])
+		[#include <X11/Xlib.h>])
 	if test x"$acx_dpms_lib_ok" = xyes; then
-		AC_CHECK_HEADERS([X11/extensions/dpms.h],,,
-			[#include <X11/Xlib.h>])
+		AC_CHECK_LIB(Xext,
+			DPMSQueryExtension,
+			[true],
+			[AC_DEFINE(HAVE_X11_EXTENSIONS_DPMS_H, 0)],
+			[$X_LIBS -lX11 $X_EXTRA_LIBS])
 	fi
 	CPPFLAGS="$save_CPPFLAGS"
 	ARCH_LIBS="$X_LIBS $X_PRE_LIBS -lXext -lX11 $X_EXTRA_LIBS $ARCH_LIBS"
diff --git a/lib/arch/CArchNetworkBSD.h b/lib/arch/CArchNetworkBSD.h
index 671e653e..3915b3ff 100644
--- a/lib/arch/CArchNetworkBSD.h
+++ b/lib/arch/CArchNetworkBSD.h
@@ -24,7 +24,7 @@
 #	include <sys/socket.h>
 #endif
 
-#if !defined(HAVE_SOCKLEN_T)
+#if !HAVE_SOCKLEN_T
 typedef int socklen_t;
 #endif
 
diff --git a/lib/common/stdistream.h b/lib/common/stdistream.h
index bd903578..33667398 100644
--- a/lib/common/stdistream.h
+++ b/lib/common/stdistream.h
@@ -13,7 +13,7 @@
  */
 
 #include "stdpre.h"
-#if defined(HAVE_ISTREAM)
+#if HAVE_ISTREAM
 #include <istream>
 #else
 #include <iostream>
diff --git a/lib/common/stdostream.h b/lib/common/stdostream.h
index e7496f5b..48e89862 100644
--- a/lib/common/stdostream.h
+++ b/lib/common/stdostream.h
@@ -13,7 +13,7 @@
  */
 
 #include "stdpre.h"
-#if defined(HAVE_OSTREAM)
+#if HAVE_OSTREAM
 #include <ostream>
 #else
 #include <iostream>
diff --git a/lib/common/stdsstream.h b/lib/common/stdsstream.h
index ed8e723f..45b28124 100644
--- a/lib/common/stdsstream.h
+++ b/lib/common/stdsstream.h
@@ -14,7 +14,7 @@
 
 #include "stdpre.h"
 
-#if defined(HAVE_SSTREAM) || !defined(__GNUC__) || (__GNUC__ >= 3)
+#if HAVE_SSTREAM || !defined(__GNUC__) || (__GNUC__ >= 3)
 
 #include <sstream>
 
diff --git a/lib/platform/CXWindowsClipboard.h b/lib/platform/CXWindowsClipboard.h
index 25c221bd..5fe126f8 100644
--- a/lib/platform/CXWindowsClipboard.h
+++ b/lib/platform/CXWindowsClipboard.h
@@ -20,7 +20,7 @@
 #include "stdmap.h"
 #include "stdlist.h"
 #include "stdvector.h"
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/Xlib.h>
diff --git a/lib/platform/CXWindowsEventQueueBuffer.h b/lib/platform/CXWindowsEventQueueBuffer.h
index 9c2bdfa3..5d9b6dd4 100644
--- a/lib/platform/CXWindowsEventQueueBuffer.h
+++ b/lib/platform/CXWindowsEventQueueBuffer.h
@@ -18,7 +18,7 @@
 #include "IEventQueueBuffer.h"
 #include "CMutex.h"
 #include "stdvector.h"
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/Xlib.h>
diff --git a/lib/platform/CXWindowsKeyState.cpp b/lib/platform/CXWindowsKeyState.cpp
index c0ec6f75..09058653 100644
--- a/lib/platform/CXWindowsKeyState.cpp
+++ b/lib/platform/CXWindowsKeyState.cpp
@@ -16,7 +16,7 @@
 #include "CXWindowsUtil.h"
 #include "CLog.h"
 #include "CStringUtil.h"
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/X.h>
@@ -92,7 +92,7 @@
 #endif
 
 // map special KeyID keys to KeySyms
-#if defined(HAVE_X11_XF86KEYSYM_H)
+#if HAVE_X11_XF86KEYSYM_H
 static const KeySym		g_mapE000[] =
 {
 	/* 0x00 */ 0, XF86XK_Eject, 0, 0, 0, 0, 0, 0,
@@ -647,7 +647,7 @@ CXWindowsKeyState::keyIDToKeySym(KeyID id, KeyModifierMask mask) const
 	if ((id & 0xfffff000) == 0xe000) {
 		// special character
 		switch (id & 0x0000ff00) {
-#if defined(HAVE_X11_XF86KEYSYM_H)
+#if HAVE_X11_XF86KEYSYM_H
 		case 0xe000:
 			return g_mapE000[id & 0xff];
 #endif
diff --git a/lib/platform/CXWindowsKeyState.h b/lib/platform/CXWindowsKeyState.h
index 36abeeb2..15d8f894 100644
--- a/lib/platform/CXWindowsKeyState.h
+++ b/lib/platform/CXWindowsKeyState.h
@@ -17,11 +17,11 @@
 
 #include "CKeyState.h"
 #include "stdmap.h"
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/Xlib.h>
-#	if defined(HAVE_X11_EXTENSIONS_XTEST_H)
+#	if HAVE_X11_EXTENSIONS_XTEST_H
 #		include <X11/extensions/XTest.h>
 #	else
 #		error The XTest extension is required to build synergy
diff --git a/lib/platform/CXWindowsScreen.cpp b/lib/platform/CXWindowsScreen.cpp
index 86d9a780..082e9a0e 100644
--- a/lib/platform/CXWindowsScreen.cpp
+++ b/lib/platform/CXWindowsScreen.cpp
@@ -26,14 +26,14 @@
 #include "IEventQueue.h"
 #include "TMethodEventJob.h"
 #include <cstring>
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/X.h>
 #	include <X11/Xutil.h>
 #	define XK_XKB_KEYS
 #	include <X11/keysymdef.h>
-#	if defined(HAVE_X11_EXTENSIONS_XTEST_H)
+#	if HAVE_X11_EXTENSIONS_XTEST_H
 #		include <X11/extensions/XTest.h>
 #	else
 #		error The XTest extension is required to build synergy
diff --git a/lib/platform/CXWindowsScreen.h b/lib/platform/CXWindowsScreen.h
index f9adfd9d..131cfb60 100644
--- a/lib/platform/CXWindowsScreen.h
+++ b/lib/platform/CXWindowsScreen.h
@@ -17,7 +17,7 @@
 
 #include "CPlatformScreen.h"
 #include "stdvector.h"
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/Xlib.h>
diff --git a/lib/platform/CXWindowsScreenSaver.cpp b/lib/platform/CXWindowsScreenSaver.cpp
index 0b69f08f..222c9a31 100644
--- a/lib/platform/CXWindowsScreenSaver.cpp
+++ b/lib/platform/CXWindowsScreenSaver.cpp
@@ -20,12 +20,12 @@
 #include "IEventQueue.h"
 #include "TMethodEventJob.h"
 #include <X11/Xatom.h>
-#if defined(HAVE_X11_EXTENSIONS_XTEST_H)
+#if HAVE_X11_EXTENSIONS_XTEST_H
 #	include <X11/extensions/XTest.h>
 #else
 #	error The XTest extension is required to build synergy
 #endif
-#if defined(HAVE_X11_EXTENSIONS_DPMS_H)
+#if HAVE_X11_EXTENSIONS_DPMS_H
 extern "C" {
 #	include <X11/Xmd.h>
 #	include <X11/extensions/dpms.h>
@@ -60,7 +60,7 @@ CXWindowsScreenSaver::CXWindowsScreenSaver(
 
 	// check for DPMS extension.  this is an alternative screen saver
 	// that powers down the display.
-#if defined(HAVE_X11_EXTENSIONS_DPMS_H)
+#if HAVE_X11_EXTENSIONS_DPMS_H
 	int eventBase, errorBase;
 	if (DPMSQueryExtension(m_display, &eventBase, &errorBase)) {
 		if (DPMSCapable(m_display)) {
@@ -509,7 +509,7 @@ CXWindowsScreenSaver::handleDisableTimer(const CEvent&, void*)
 void
 CXWindowsScreenSaver::activateDPMS(bool activate)
 {
-#if defined(HAVE_X11_EXTENSIONS_DPMS_H)
+#if HAVE_X11_EXTENSIONS_DPMS_H
 	if (m_dpms) {
 		// DPMSForceLevel will generate a BadMatch if DPMS is disabled
 		CXWindowsUtil::CErrorLock lock(m_display);
@@ -521,7 +521,7 @@ CXWindowsScreenSaver::activateDPMS(bool activate)
 void
 CXWindowsScreenSaver::enableDPMS(bool enable)
 {
-#if defined(HAVE_X11_EXTENSIONS_DPMS_H)
+#if HAVE_X11_EXTENSIONS_DPMS_H
 	if (m_dpms) {
 		if (enable) {
 			DPMSEnable(m_display);
@@ -536,7 +536,7 @@ CXWindowsScreenSaver::enableDPMS(bool enable)
 bool
 CXWindowsScreenSaver::isDPMSEnabled() const
 {
-#if defined(HAVE_X11_EXTENSIONS_DPMS_H)
+#if HAVE_X11_EXTENSIONS_DPMS_H
 	if (m_dpms) {
 		CARD16 level;
 		BOOL state;
@@ -554,7 +554,7 @@ CXWindowsScreenSaver::isDPMSEnabled() const
 bool
 CXWindowsScreenSaver::isDPMSActivated() const
 {
-#if defined(HAVE_X11_EXTENSIONS_DPMS_H)
+#if HAVE_X11_EXTENSIONS_DPMS_H
 	if (m_dpms) {
 		CARD16 level;
 		BOOL state;
diff --git a/lib/platform/CXWindowsScreenSaver.h b/lib/platform/CXWindowsScreenSaver.h
index 20c2237d..193e1e7b 100644
--- a/lib/platform/CXWindowsScreenSaver.h
+++ b/lib/platform/CXWindowsScreenSaver.h
@@ -17,7 +17,7 @@
 
 #include "IScreenSaver.h"
 #include "stdmap.h"
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/Xlib.h>
diff --git a/lib/platform/CXWindowsUtil.h b/lib/platform/CXWindowsUtil.h
index fb3fb9e7..5765c94a 100644
--- a/lib/platform/CXWindowsUtil.h
+++ b/lib/platform/CXWindowsUtil.h
@@ -19,7 +19,7 @@
 #include "BasicTypes.h"
 #include "stdmap.h"
 #include "stdvector.h"
-#if defined(X_DISPLAY_MISSING)
+#if X_DISPLAY_MISSING
 #	error X11 is required to build synergy
 #else
 #	include <X11/Xlib.h>