diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 8b61b43339..878696add8 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -213,6 +213,9 @@ pub fn (mut c Checker) check_files(ast_files []ast.File) {
 			c.error('a _test.v file should have *at least* one `test_` function', token.Position{})
 		}
 	}
+	if c.pref.skip_unused {
+		c.mark_used(ast_files)
+	}
 	// Make sure fn main is defined in non lib builds
 	if c.pref.build_mode == .build_module || c.pref.is_test {
 		return
@@ -227,9 +230,6 @@ pub fn (mut c Checker) check_files(ast_files []ast.File) {
 	} else if !has_main_fn {
 		c.error('function `main` must be declared in the main module', token.Position{})
 	}
-	if c.pref.skip_unused {
-		c.mark_used(ast_files)
-	}
 }
 
 // do checks specific to files in main module
diff --git a/vlib/v/checker/mark_used.v b/vlib/v/checker/mark_used.v
index 50ac93f73d..5866019216 100644
--- a/vlib/v/checker/mark_used.v
+++ b/vlib/v/checker/mark_used.v
@@ -85,6 +85,21 @@ fn (mut c Checker) mark_used(ast_files []ast.File) {
 	c.table.used_fns['main.main'] = true
 	c.table.used_fns['builtin_init'] = true
 	c.table.used_fns['memdup'] = true
+	c.table.used_fns['vstring'] = true
+	c.table.used_fns['vstring_with_len'] = true
+	c.table.used_fns['string'] = true // array.string
+	// c.table.used_fns['str'] = true // builtin .str() methods; They use strings.builder and strconv.ftoa_64 etc.
+	// whitelist common modules const initializers too:
+	c.table.used_fns['os.getwd'] = true
+	c.table.used_fns['os.init_os_args'] = true
+	//
+	c.table.used_fns['term.can_show_color_on_stdin'] = true
+	c.table.used_fns['term.can_show_color_on_stdout'] = true
+	c.table.used_fns['term.can_show_color_on_stderr'] = true
+	//
+	c.table.used_fns['main.can_use_relative_paths'] = true
+	//
+	// eprintln('>>> c.table.used_fns: $c.table.used_fns')
 	// c.timing_measure(@FN)
 
 	// println(walker.used_fns)