diff --git a/AMBuildScript b/AMBuildScript
index 4506cbb..120ddbd 100644
--- a/AMBuildScript
+++ b/AMBuildScript
@@ -13,23 +13,25 @@ class MMS:
 		                              'name': 'EPISODEONE',     'platform': ['windows', 'linux']}
 		self.possibleSdks['ep2'] =   {'sdk': 'HL2SDKOB',        'ext': '2.ep2',   'def': '3',
 		                              'name': 'ORANGEBOX',      'platform': ['windows', 'linux']}
-		self.possibleSdks['ep2v'] =  {'sdk': 'HL2SDKOBVALVE',   'ext': '2.ep2v',  'def': '6',
+		self.possibleSdks['css'] =   {'sdk': 'HL2SDKCSS',       'ext': '2.css',  'def': '6',
+		                              'name': 'CSS',            'platform': ['windows', 'linux', 'darwin']}
+		self.possibleSdks['ep2v'] =  {'sdk': 'HL2SDKOBVALVE',   'ext': '2.ep2v',  'def': '7',
 		                              'name': 'ORANGEBOXVALVE', 'platform': ['windows', 'linux', 'darwin']}
-		self.possibleSdks['l4d'] =   {'sdk': 'HL2SDKL4D',       'ext': '2.l4d',   'def': '7',
+		self.possibleSdks['l4d'] =   {'sdk': 'HL2SDKL4D',       'ext': '2.l4d',   'def': '8',
 		                              'name': 'LEFT4DEAD',      'platform': ['windows', 'linux', 'darwin']}
-		self.possibleSdks['l4d2'] =  {'sdk': 'HL2SDKL4D2',      'ext': '2.l4d2',  'def': '8',
+		self.possibleSdks['l4d2'] =  {'sdk': 'HL2SDKL4D2',      'ext': '2.l4d2',  'def': '9',
 		                              'name': 'LEFT4DEAD2',     'platform': ['windows', 'linux', 'darwin']}
 		self.possibleSdks['darkm'] = {'sdk': 'HL2SDK-DARKM',    'ext': '2.darkm', 'def': '2',
 		                              'name': 'DARKMESSIAH',    'platform': ['windows']}
-		self.possibleSdks['swarm'] = {'sdk': 'HL2SDK-SWARM',    'ext': '2.swarm', 'def': '9',
+		self.possibleSdks['swarm'] = {'sdk': 'HL2SDK-SWARM',    'ext': '2.swarm', 'def': '10',
 		                              'name': 'ALIENSWARM',     'platform': ['windows']}
 		self.possibleSdks['bgt'] =   {'sdk': 'HL2SDK-BGT',      'ext': '2.bgt', 'def': '4',
 		                              'name': 'BLOODYGOODTIME', 'platform': ['windows']}
 		self.possibleSdks['eye'] =   {'sdk': 'HL2SDK-EYE',      'ext': '2.eye', 'def': '5',
 		                              'name': 'EYE', 'platform': ['windows']}
-		self.possibleSdks['csgo'] =   {'sdk': 'HL2SDKCSGO',      'ext': '2.csgo', 'def': '11',
+		self.possibleSdks['csgo'] =   {'sdk': 'HL2SDKCSGO',      'ext': '2.csgo', 'def': '12',
 		                              'name': 'CSGO', 'platform': ['windows', 'linux']}
-		# self.possibleSdks['portal2'] =   {'sdk': 'HL2SDK-PORTAL2',      'ext': '2.portal2', 'def': '10',
+		# self.possibleSdks['portal2'] =   {'sdk': 'HL2SDK-PORTAL2',      'ext': '2.portal2', 'def': '11',
 		#                               'name': 'PORTAL2', 'platform': ['windows']}
 		
 		self.sdkInfo = { }
@@ -45,6 +47,7 @@ class MMS:
 				envvars['HL2SDKOB'] = 'hl2sdk-ob'
 				envvars['HL2SDKCSGO'] = 'hl2sdk-csgo'
 
+			envvars['HL2SDKCSS'] = 'hl2sdk-css'
 			envvars['HL2SDKOBVALVE'] = 'hl2sdk-ob-valve'
 			envvars['HL2SDKL4D'] = 'hl2sdk-l4d'
 			envvars['HL2SDKL4D2'] = 'hl2sdk-l4d2'
@@ -261,7 +264,7 @@ class MMS:
 			else:
 				staticLibs = os.path.join(sdkPath, 'lib', 'linux')
 			workFolder = os.path.join(AMBuild.outputFolder, job.workFolder)
-			if sdk in ['ep2v', 'l4d', 'l4d2', 'csgo']:
+			if sdk in ['css', 'ep2v', 'l4d', 'l4d2', 'csgo']:
 				libs = ['tier1_i486.a', 'libvstdlib.so', 'libtier0.so']
 				if sdk == 'csgo':
 					libs.insert(0, 'interfaces_i486.a')
@@ -320,7 +323,7 @@ class MMS:
 		
 		# We don't build for Portal 2 (yet?, ever?), but using this define in code as 
 		# it saves trouble if we ever need to
-		compiler['CDEFINES'].append('SE_PORTAL2=10')
+		compiler['CDEFINES'].append('SE_PORTAL2=11')
 
 		paths = [['public'], ['public', 'engine'], ['public', 'mathlib'], ['public', 'vstdlib'],
 						 ['public', 'tier0'], ['public', 'tier1']]
@@ -358,7 +361,7 @@ class MMS:
 		if not noLink:
 			if AMBuild.target['platform'] == 'linux':
 				compiler['POSTLINKFLAGS'][0:0] = ['-lm']
-				if sdk in ['ep2v', 'l4d', 'l4d2', 'csgo']:
+				if sdk in ['css', 'ep2v', 'l4d', 'l4d2', 'csgo']:
 					compiler['POSTLINKFLAGS'][0:0] = ['libtier0.so']
 					compiler['POSTLINKFLAGS'][0:0] = ['libvstdlib.so']
 				else:
diff --git a/core/ISmmPluginExt.h b/core/ISmmPluginExt.h
index 9313526..b89e464 100644
--- a/core/ISmmPluginExt.h
+++ b/core/ISmmPluginExt.h
@@ -41,13 +41,14 @@
 #define SOURCE_ENGINE_ORANGEBOX			3				/**< Orange Box Source Engine (third major SDK) */
 #define SOURCE_ENGINE_LEFT4DEAD			4				/**< Left 4 Dead */
 #define SOURCE_ENGINE_DARKMESSIAH		5				/**< Dark Messiah Multiplayer (based on original engine) */
-#define SOURCE_ENGINE_ORANGEBOXVALVE	6				/**< Orange Box Source Engine for Valve games (TF2/DOD:S) */
+#define SOURCE_ENGINE_ORANGEBOXVALVE	6				/**< Orange Box Source Engine for Valve games (TF2/DOD:S/HL2DM) */
 #define SOURCE_ENGINE_LEFT4DEAD2		7				/**< Left 4 Dead 2 */
 #define SOURCE_ENGINE_ALIENSWARM		8				/**< Alien Swarm */
 #define SOURCE_ENGINE_BLOODYGOODTIME	9				/**< Bloody Good Time */
 #define SOURCE_ENGINE_EYE				10				/**< E.Y.E Divine Cybermancy */
 #define SOURCE_ENGINE_PORTAL2			11				/**< Portal 2 */
 #define SOURCE_ENGINE_CSGO				12				/**< Counter-Strike: Global Offensive */
+#define SOURCE_ENGINE_CSS				13				/**< Counter-Strike: Source (sometimes older version of Orange Box Valve) */
 
 #define METAMOD_PLAPI_VERSION			15				/**< Version of this header file */
 #define METAMOD_PLAPI_NAME				"ISmmPlugin"	/**< Name of the plugin interface */
diff --git a/core/metamod_console.cpp b/core/metamod_console.cpp
index f0e2b1e..ff4c552 100644
--- a/core/metamod_console.cpp
+++ b/core/metamod_console.cpp
@@ -121,6 +121,8 @@ bool Command_Meta(IMetamodSourceCommandInfo *info)
 			CONMSG("  Engine: Left 4 Dead (2008)\n");
 #elif SOURCE_ENGINE == SE_ORANGEBOX
 			CONMSG("  Engine: Episode 2 (Orange Box, 2007)\n");
+#elif SOURCE_ENGINE == SE_CSS
+			CONMSG("  Engine: Counter-Strike: Source (Old Valve Orange Box, 2009)\n");
 #elif SOURCE_ENGINE == SE_ORANGEBOXVALVE
 			CONMSG("  Engine: Episode 2 (Valve Orange Box, 2009)\n");
 #elif SOURCE_ENGINE == SE_DARKMESSIAH
diff --git a/core/provider/provider_ep2.cpp b/core/provider/provider_ep2.cpp
index 1c1bee0..72c70ab 100644
--- a/core/provider/provider_ep2.cpp
+++ b/core/provider/provider_ep2.cpp
@@ -367,6 +367,8 @@ int BaseProvider::DetermineSourceEngine(const char *game)
 	return SOURCE_ENGINE_LEFT4DEAD;
 #elif SOURCE_ENGINE == SE_ORANGEBOX
 	return SOURCE_ENGINE_ORANGEBOX;
+#elif SOURCE_ENGINE == SE_CSS
+	return SOURCE_ENGINE_CSS;
 #elif SOURCE_ENGINE == SE_ORANGEBOXVALVE
 	return SOURCE_ENGINE_ORANGEBOXVALVE;
 #elif SOURCE_ENGINE == SE_DARKMESSIAH
diff --git a/loader/loader.cpp b/loader/loader.cpp
index 0b63c32..4a8b204 100644
--- a/loader/loader.cpp
+++ b/loader/loader.cpp
@@ -75,6 +75,7 @@ static const char *backend_names[] =
 	"2.ep2",
 	"2.bgt",
 	"2.eye",
+	"2.css",
 	"2.ep2v",
 	"2.l4d",
 	"2.l4d2",
@@ -313,6 +314,10 @@ mm_DetermineBackend(QueryValveInterface engineFactory, const char *game_name)
 				{
 					return MMBackend_EYE;
 				}
+				else if (strcmp(game_name, "cstrike") == 0)
+				{
+					return MMBackend_CSS;
+				}
 				else
 				{
 					return MMBackend_Episode2Valve;
diff --git a/loader/loader.h b/loader/loader.h
index 8963c1e..9544c57 100644
--- a/loader/loader.h
+++ b/loader/loader.h
@@ -85,6 +85,7 @@ enum MetamodBackend
 	MMBackend_Episode2,
 	MMBackend_BloodyGoodTime,
 	MMBackend_EYE,
+	MMBackend_CSS,
 	MMBackend_Episode2Valve,
 	MMBackend_Left4Dead,
 	MMBackend_Left4Dead2,