diff --git a/compiler/comptime.v b/compiler/comptime.v
index c2d4bed885..b0286e1763 100644
--- a/compiler/comptime.v
+++ b/compiler/comptime.v
@@ -30,7 +30,31 @@ fn (p mut Parser) comp_time() {
 				p.genln('#ifdef $ifdef_name')
 			}
 			p.check(.lcbr)
-			p.statements_no_rcbr()
+			os := os_from_string(name)
+			if p.fileis('runtime.v') && os != p.os {
+				// `$if os {` for a different target, skip everything inside
+				// to avoid compilation errors (like including <windows.h>
+				// on non-Windows systems)
+				mut stack := 1
+				for {
+					if p.tok == .lcbr {
+						stack++
+					} else if p.tok == .rcbr {
+						stack--
+					}	
+					if p.tok == .eof {
+						break
+					}	
+					if stack <= 0 && p.tok == .rcbr {
+						//p.warn('exiting $stack')
+						p.next()
+						break
+					}	
+					p.next()
+				}	
+			}	 else {
+				p.statements_no_rcbr()
+			}
 			if ! (p.tok == .dollar && p.peek() == .key_else) {
 				p.genln('#endif')
 			}
diff --git a/compiler/main.v b/compiler/main.v
index 605fded22c..93bb63002e 100644
--- a/compiler/main.v
+++ b/compiler/main.v
@@ -529,18 +529,15 @@ fn (v mut V) gen_main_end(return_statement string){
 }
 
 fn final_target_out_name(out_name string) string {
-	mut cmd := if out_name.starts_with('/') {
+	$if windows {
+		return out_name.replace('/', '\\') + '.exe'
+	}
+	return if out_name.starts_with('/') {
 		out_name
 	}
 	else {
 		'./' + out_name
 	}
-	$if windows {
-		cmd = out_name
-		cmd = cmd.replace('/', '\\')
-		cmd += '.exe'
-	}
-	return cmd
 }
 
 fn (v V) run_compiled_executable_and_exit() {
@@ -895,18 +892,7 @@ fn new_v(args[]string) &V {
 		}
 	}
 	else {
-		switch target_os {
-		case 'linux': _os = .linux
-		case 'windows': _os = .windows
-		case 'mac': _os = .mac
-		case 'freebsd': _os = .freebsd
-		case 'openbsd': _os = .openbsd
-		case 'netbsd': _os = .netbsd
-		case 'dragonfly': _os = .dragonfly
-		case 'msvc': _os = .msvc
-		case 'js': _os = .js
-		case 'solaris': _os = .solaris
-		}
+		_os = os_from_string(target_os)
 	}
 	// Location of all vlib files
 	vroot := os.dir(os.executable())
@@ -1097,3 +1083,21 @@ fn vhash() string {
 fn cescaped_path(s string) string {
   return s.replace('\\','\\\\')
 }
+
+fn os_from_string(os string) OS {
+	switch os {
+		case 'linux': return .linux
+		case 'windows': return .windows
+		case 'mac': return .mac
+		case 'freebsd': return .freebsd
+		case 'openbsd': return .openbsd
+		case 'netbsd': return .netbsd
+		case 'dragonfly': return .dragonfly
+		case 'msvc': return .msvc
+		case 'js': return .js
+		case 'solaris': return .solaris
+		case 'android': return .android
+		}
+	println('bad os $os') // todo panic?
+	return .linux
+}
diff --git a/vlib/runtime/runtime.v b/vlib/runtime/runtime.v
index 7777c00615..2d11a30730 100644
--- a/vlib/runtime/runtime.v
+++ b/vlib/runtime/runtime.v
@@ -1 +1,14 @@
 module runtime
+
+$if linux {
+	#include <sys/sysinfo.h>
+	fn C.get_nprocs() int
+}
+
+
+pub fn nr_cpus() int {
+	$if linux {
+		return C.get_nprocs()
+	}
+	return 0
+}
diff --git a/vlib/runtime/runtime_mac.v b/vlib/runtime/runtime_mac.v
index 7345c63217..9df2fff173 100644
--- a/vlib/runtime/runtime_mac.v
+++ b/vlib/runtime/runtime_mac.v
@@ -1,5 +1,2 @@
 module runtime
 
-pub fn nr_cpus() int {
-	return 0
-}
diff --git a/vlib/runtime/runtime_test.v b/vlib/runtime/runtime_test.v
index 639a86eb59..cd0bb6e58a 100644
--- a/vlib/runtime/runtime_test.v
+++ b/vlib/runtime/runtime_test.v
@@ -2,8 +2,8 @@ import runtime
 
 fn test_nr_cpus() {
 	$if linux {
-	nr_cpus := runtime.nr_cpus()
-	println(nr_cpus)
-	assert nr_cpus > 0
+		nr_cpus := runtime.nr_cpus()
+		println(nr_cpus)
+		assert nr_cpus > 0
 	}
 }	
diff --git a/vlib/runtime/runtime_win.v b/vlib/runtime/runtime_win.v
index 7345c63217..9df2fff173 100644
--- a/vlib/runtime/runtime_win.v
+++ b/vlib/runtime/runtime_win.v
@@ -1,5 +1,2 @@
 module runtime
 
-pub fn nr_cpus() int {
-	return 0
-}