diff --git a/compiler/cc.v b/compiler/cc.v
index aa6c7e5d57..4f4b1b79dd 100644
--- a/compiler/cc.v
+++ b/compiler/cc.v
@@ -106,25 +106,29 @@ fn (v mut V) cc() {
 		a << f
 	}
 
-	libs := ''// builtin.o os.o http.o etc
+	mut libs := ''// builtin.o os.o http.o etc
 	if v.pref.build_mode == .build_module {
 		a << '-c'
 	}
-	else if v.pref.build_mode == .default_mode {
+	else if v.pref.is_debug {
+		libs = '$v_modules_path/vlib/builtin.o ' +
+		 '$v_modules_path/vlib/strings.o '+
+		 '$v_modules_path/vlib/math.o '
 		/*
-		// TODO
-		libs = '$v_modules_path/vlib/builtin.o'
 		if !os.file_exists(libs) {
 			println('object file `$libs` not found')
 			exit(1)
 		}
+		*/
 		for imp in v.table.imports {
 			if imp == 'webview' {
 				continue
 			}
-			libs += ' "$v_modules_path/vlib/${imp}.o"'
+			path := 	'"$v_modules_path/vlib/${imp}.o"'
+			if os.file_exists(path) {
+				libs += ' ' + path
+			}
 		}
-		*/
 	}
 	if v.pref.sanitize {
 		a << '-fsanitize=leak'
diff --git a/compiler/module_header.v b/compiler/module_header.v
index 058d69d33a..86edf0ac56 100644
--- a/compiler/module_header.v
+++ b/compiler/module_header.v
@@ -11,7 +11,7 @@ import (
 
 /*
 	.vh generation logic.
-	.vh files contains only function signatures, consts, and types.
+	.vh files contain only function signatures, consts, and types.
 	They are used together with pre-compiled modules.
 */
 
@@ -95,7 +95,11 @@ fn v_type_str(typ_ string) string {
 		return '[]' + typ.right(6)
 	}	
 	if typ.contains('__') {
-		return typ.all_after('__')
+		opt := typ.starts_with('?')
+		typ = typ.all_after('__')
+		if opt {
+			typ = '?' + typ
+		}	
 	}	
 	return typ
 }	
@@ -213,8 +217,8 @@ fn (v &V) generate_vh() {
 	// Methods
 	file.writeln('\n// Methods //////////////////')
 	for _, typ in v.table.typesmap {
-		if typ.mod != v.mod { //&& typ.mod != '' {
-			//println('skipping method typ $typ.name mod=$typ.mod')
+		if typ.mod != v.mod && !(v.mod == 'builtin' && typ.mod == '') {
+			println('skipping method typ $typ.name mod=$typ.mod')
 			continue
 		}	
 		for method in typ.methods {
diff --git a/compiler/parser.v b/compiler/parser.v
index 18dd91fab7..ab814b856f 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -509,6 +509,8 @@ fn (p mut Parser) const_decl() {
 			// .vh files don't have const values, just types: `const (a int)`
 			typ = p.get_type()
 			p.table.register_const(name, typ, p.mod)
+			p.cgen.consts << ('extern ' +
+				p.table.cgen_name_type_pair(name, typ)) + ';'
 			continue // Don't generate C code when building a .vh file
 		} else {
 			p.check_space(.assign)
@@ -524,7 +526,9 @@ fn (p mut Parser) const_decl() {
 			// TODO hack
 			// cur_line has const's value right now. if it's just a number, then optimize generation:
 			// output a #define so that we don't pollute the binary with unnecessary global vars
-			if is_compile_time_const(p.cgen.cur_line) {
+			// Do not do this when building a module, otherwise the consts
+			// will not be accessible.
+			if p.pref.build_mode != .build_module && is_compile_time_const(p.cgen.cur_line) {
 				p.cgen.consts << '#define $name $p.cgen.cur_line'
 				p.cgen.resetln('')
 				p.fgenln('')