diff --git uppsrc/umk/umake.cpp uppsrc/umk/umake.cpp
--- uppsrc/umk/umake.cpp
+++ uppsrc/umk/umake.cpp
@@ -85,6 +85,7 @@ CONSOLE_APP_MAIN
 	int  exporting = 0;
 	bool run = false;
 	String mkf;
+	String platformFlags;
 
 	Vector<String> param, runargs;
 	
@@ -129,9 +130,38 @@ CONSOLE_APP_MAIN
 					ide.console.SetSlots(n);
 					break;
 				}
+				case 't': {
+					if(s[1] == '=') {
+						static const VectorMap<String, String> flags = {
+							{"windows", "WIN32"},
+							{"linux", "POSIX LINUX"},
+							{"android", "POSIX LINUX ANDROID"},
+							{"osx", "POSIX BSD OSX"},
+							{"osx11", "POSIX BSD OSX OSX11 X11"},
+							{"freebsd", "POSIX BSD FREEBSD"},
+							{"openbsd", "POSIX BSD OPENBSD"},
+							{"netbsd", "POSIX BSD NETBSD"},
+							{"dragonfly", "POSIX BSD DRAGONFLY"},
+							{"solaris", "POSIX SOLARIS"}
+						};
+						String p(s += 2);
+						int q = flags.Find(ToLower(p));
+						if(q >= 0)
+							platformFlags = flags[q];
+						else {
+							SilentMode = false;
+							Puts("Invalid target platform option: " << p << '\n');
+							Puts("Available target platform options:\n" << Join(flags.GetKeys(), ", ") << '\n');
+							SetExitCode(3);
+							return;
+						}
+						s += p.GetCount();
+					}
+					break;
+				}
 				default:
 					SilentMode = false;
-					Puts("Invalid build option(s)");
+					Puts("Invalid build option(s)\n");
 					SetExitCode(3);
 					return;
 				}
@@ -202,6 +232,22 @@ CONSOLE_APP_MAIN
 			if(f.GetCount())
 				ide.mainconfigparam = f[0].param;
 		}
+		if(!IsNull(platformFlags)) {
+			if(!IsNull(ide.mainconfigparam)) {
+				Vector<String> a = Split(platformFlags, ' '),
+					b = Split(ide.mainconfigparam, ' ');
+				const int n = b.GetCount();
+				for(int i = n - 1; i >= 0; --i)
+					for(const String& p : a)
+						if(p == b[i])
+							b.Remove(i);
+				if(n != b.GetCount())
+					ide.mainconfigparam = Join(b, " ");
+				if(!IsNull(ide.mainconfigparam))
+					ide.mainconfigparam.Insert(0, ' ');
+			}
+			ide.mainconfigparam.Insert(0, platformFlags);
+		}
 		PutVerbose("Build flags: " << ide.mainconfigparam);
 		String m = 2 < param.GetCount() ? param[2] : "CLANG";
 		String bp = GetBuildMethodPath(m);
@@ -260,7 +306,7 @@ CONSOLE_APP_MAIN
 			SetExitCode(1);
 	}
 	else
-		Puts("Usage: [-options] umk assembly main_package [build_method] [+flags] [output]\n\n"
+		Puts("Usage: umk assembly main_package [build_method] [-options] [+flags] [output]\n\n"
 		     "Examples: umk examples Bombs GCC -ab +GUI,SHARED ~/bombs\n"
 		     "          umk examples,uppsrc Bombs ~/GCC.bm -rv +GUI,SHARED ~/bin\n\n"
 		     "See http://www.ultimatepp.org/app$ide$umk$en-us.html for details\n");