Index: source/ps/ConfigDB.h
===================================================================
--- source/ps/ConfigDB.h
+++ source/ps/ConfigDB.h
@@ -41,6 +41,7 @@
 	CFG_MOD,
 	CFG_USER,
 	CFG_COMMAND,
+	CFG_SANITIZE,
 	CFG_LAST
 };
 
@@ -59,7 +60,7 @@
 
 	/**
 	 * Attempt to retrieve the value of a config variable with the given name;
-	 * will search CFG_COMMAND first, and then all namespaces from the specified
+	 * will search CFG_SANITIZE first, and then all namespaces from the specified
 	 * namespace down.
 	 */
 	void GetValue(EConfigNamespace ns, const CStr& name, bool& value);
@@ -81,7 +82,7 @@
 
 	/**
 	 * Attempt to retrieve a vector of values corresponding to the given setting;
-	 * will search CFG_COMMAND first, and then all namespaces from the specified
+	 * will search CFG_SANITIZE first, and then all namespaces from the specified
 	 * namespace down.
 	 */
 	void GetValues(EConfigNamespace ns, const CStr& name, CConfigValueSet& values) const;
@@ -107,6 +108,10 @@
 
 	void SetValueBool(EConfigNamespace ns, const CStr& name, const bool value);
 
+	void SetValueInt(EConfigNamespace ns, const CStr& name, const int value);
+
+	void SetValueDouble(EConfigNamespace ns, const CStr& name, const double value);
+
 	/**
 	 * Remove a config value in the specified namespace.
 	 */
Index: source/ps/ConfigDB.cpp
===================================================================
--- source/ps/ConfigDB.cpp
+++ source/ps/ConfigDB.cpp
@@ -92,8 +92,8 @@
 	{\
 		CHECK_NS(;);\
 		CScopeLock s(&cfgdb_mutex);\
-		TConfigMap::iterator it = m_Map[CFG_COMMAND].find(name);\
-		if (it != m_Map[CFG_COMMAND].end())\
+		TConfigMap::iterator it = m_Map[CFG_SANITIZE].find(name);\
+		if (it != m_Map[CFG_SANITIZE].end())\
 		{\
 			Get(it->second[0], value);\
 			return;\
@@ -136,8 +136,8 @@
 	CHECK_NS(;);
 
 	CScopeLock s(&cfgdb_mutex);
-	TConfigMap::iterator it = m_Map[CFG_COMMAND].find(name);
-	if (it != m_Map[CFG_COMMAND].end())
+	TConfigMap::iterator it = m_Map[CFG_SANITIZE].find(name);
+	if (it != m_Map[CFG_SANITIZE].end())
 	{
 		values = it->second;
 		return;
@@ -159,9 +159,9 @@
 	CHECK_NS(CFG_LAST);
 
 	CScopeLock s(&cfgdb_mutex);
-	TConfigMap::iterator it = m_Map[CFG_COMMAND].find(name);
-	if (it != m_Map[CFG_COMMAND].end())
-		return CFG_COMMAND;
+	TConfigMap::iterator it = m_Map[CFG_SANITIZE].find(name);
+	if (it != m_Map[CFG_SANITIZE].end())
+		return CFG_SANITIZE;
 
 	for (int search_ns = ns; search_ns >= 0; --search_ns)
 	{
@@ -187,7 +187,7 @@
 			if (boost::algorithm::starts_with(p.first, prefix))
 				ret[p.first] = p.second;
 
-	for (const std::pair<CStr, CConfigValueSet>& p : m_Map[CFG_COMMAND])
+	for (const std::pair<CStr, CConfigValueSet>& p : m_Map[CFG_SANITIZE])
 		if (boost::algorithm::starts_with(p.first, prefix))
 			ret[p.first] = p.second;
 
@@ -212,6 +212,18 @@
 	SetValueString(ns, name, valueString);
 }
 
+void CConfigDB::SetValueInt(EConfigNamespace ns, const CStr& name, const int value)
+{
+	CStr valueString = CStr::FromInt(value);
+	SetValueString(ns, name, valueString);
+}
+
+void CConfigDB::SetValueDouble(EConfigNamespace ns, const CStr& name, const double value)
+{
+	CStr valueString = CStr::FromDouble(value);
+	SetValueString(ns, name, valueString);
+}
+
 void CConfigDB::RemoveValue(EConfigNamespace ns, const CStr& name)
 {
 	CHECK_NS(;);
Index: source/ps/GameSetup/Config.cpp
===================================================================
--- source/ps/GameSetup/Config.cpp
+++ source/ps/GameSetup/Config.cpp
@@ -24,6 +24,7 @@
 #include "ps/CLogger.h"
 #include "ps/ConfigDB.h"
 #include "ps/GameSetup/CmdLineArgs.h"
+#include "ps/VideoMode.h"
 
 // (these variables are documented in the header.)
 
@@ -64,6 +65,7 @@
 int g_xres, g_yres;
 float g_GuiScale = 1.0f;
 bool g_VSync = false;
+bool g_Windowed = true;
 
 bool g_Quickstart = false;
 bool g_DisableAudio = false;
@@ -111,6 +113,7 @@
 	CFG_GET_VAL("postproc", g_PostProc);
 	CFG_GET_VAL("smoothlos", g_SmoothLOS);
 	CFG_GET_VAL("gui.scale", g_GuiScale);
+	CFG_GET_VAL("windowed", g_Windowed);
 }
 
 
@@ -135,8 +138,6 @@
 	if (args.Has("g"))
 	{
 		g_Gamma = args.Get("g").ToFloat();
-		if (g_Gamma == 0.0f)
-			g_Gamma = 1.0f;
 	}
 
 //	if (args.Has("listfiles"))
@@ -177,6 +178,39 @@
 }
 
 
+static void SanitizeConfig()
+{
+	if (g_Gamma <= 0.0)
+	{
+		g_Gamma = 1.0;
+	}
+
+	if (g_GuiScale <= 0.0)
+	{
+		g_GuiScale = 1.0;
+		g_ConfigDB.SetValueDouble(CFG_SANITIZE, "gui.scale", 1.0);
+	}
+
+	if (g_xres <= 0)
+	{
+		if(g_Windowed)
+			g_xres = DEFAULT_WINDOW_W;
+		else
+			g_xres = DEFAULT_FULLSCREEN_W;
+		g_ConfigDB.SetValueInt(CFG_SANITIZE, "xres", g_xres);
+	}
+
+	if (g_yres <= 0)
+	{
+		if(g_Windowed)
+			g_yres = DEFAULT_WINDOW_H;
+		else
+			g_yres = DEFAULT_FULLSCREEN_H;
+		g_ConfigDB.SetValueInt(CFG_SANITIZE, "yres", g_yres);
+	}
+}
+
+
 void CONFIG_Init(const CmdLineArgs& args)
 {
 	TIMER(L"CONFIG_Init");
@@ -208,4 +242,7 @@
 	// Collect information from system.cfg, the profile file,
 	// and any command-line overrides to fill in the globals.
 	LoadGlobals();	// 64ms
+
+	// Check for invalid values and sanitize them
+	SanitizeConfig();
 }
Index: source/ps/VideoMode.h
===================================================================
--- source/ps/VideoMode.h
+++ source/ps/VideoMode.h
@@ -127,4 +127,10 @@
 
 extern CVideoMode g_VideoMode;
 
+extern const int DEFAULT_WINDOW_W;
+extern const int DEFAULT_WINDOW_H;
+
+extern const int DEFAULT_FULLSCREEN_W;
+extern const int DEFAULT_FULLSCREEN_H;
+
 #endif // INCLUDED_VIDEOMODE
Index: source/ps/VideoMode.cpp
===================================================================
--- source/ps/VideoMode.cpp
+++ source/ps/VideoMode.cpp
@@ -38,11 +38,11 @@
 #endif
 
 
-static int DEFAULT_WINDOW_W = 1024;
-static int DEFAULT_WINDOW_H = 768;
+const int DEFAULT_WINDOW_W = 1024;
+const int DEFAULT_WINDOW_H = 768;
 
-static int DEFAULT_FULLSCREEN_W = 1024;
-static int DEFAULT_FULLSCREEN_H = 768;
+const int DEFAULT_FULLSCREEN_W = 1024;
+const int DEFAULT_FULLSCREEN_H = 768;
 
 CVideoMode g_VideoMode;