diff --git a/AMBuildScript b/AMBuildScript
index 2ba7ac9ee..36cd426d9 100644
--- a/AMBuildScript
+++ b/AMBuildScript
@@ -182,11 +182,13 @@ class SM:
 			#Platform-specifics
 			if AMBuild.target['platform'] == 'linux':
 				self.compiler.AddToListVar('CDEFINES', '_LINUX')
+				self.compiler.AddToListVar('CDEFINES', 'POSIX')
 				if self.vendor == 'gcc':
 					self.compiler.AddToListVar('POSTLINKFLAGS', '-static-libgcc')
 				if self.vendor == 'clang':
 					self.compiler.AddToListVar('POSTLINKFLAGS', '-lgcc_eh')
 			elif AMBuild.target['platform'] == 'darwin':
+				self.compiler.AddToListVar('CDEFINES', 'POSIX')
 				self.compiler.AddToListVar('POSTLINKFLAGS', '-mmacosx-version-min=10.5')
 				self.compiler.AddToListVar('POSTLINKFLAGS', ['-arch', 'i386'])
 				self.compiler.AddToListVar('POSTLINKFLAGS', '-lstdc++')