diff --git a/vlib/v/table/cflags.v b/vlib/v/table/cflags.v
index 476e7a5dc4..389bf9bf83 100644
--- a/vlib/v/table/cflags.v
+++ b/vlib/v/table/cflags.v
@@ -22,7 +22,7 @@ pub fn (var table Table) parse_cflag(cflg, mod string, ctimedefines []string) ?b
 	flag_orig := cflg.trim_space()
 	var flag := flag_orig
 	if flag == '' {
-		return true
+		return none
 	}
 	var fos := ''
 	var allowed_os_overrides := ['linux', 'darwin', 'freebsd', 'windows', 'mingw', 'solaris']
diff --git a/vlib/v/table/cflags_test.v b/vlib/v/table/cflags_test.v
new file mode 100644
index 0000000000..892e8acc69
--- /dev/null
+++ b/vlib/v/table/cflags_test.v
@@ -0,0 +1,75 @@
+import table
+import v.cflag
+
+const (
+	module_name = 'main'
+	cdefines    = []string
+	no_name     = ''
+	no_flag     = ''
+	no_os       = ''
+)
+
+fn test_parse_valid_cflags() {
+	t := table.new_table()
+	expected_flags := [
+		make_flag('freebsd', '-I', '/usr/local/include/freetype2'),
+		make_flag('linux', '-l', 'glfw'),
+		make_flag('mingw', no_name, '-mwindows'),
+		make_flag('solaris', '-L', '/opt/local/lib'),
+		make_flag('darwin', '-framework', 'Cocoa'),
+		make_flag('windows', '-l', 'gdi32'),
+		make_flag(no_os, '-l', 'mysqlclient'),
+		make_flag(no_os, no_name, '-test'),
+	]
+	parse_valid_flag(t, '-lmysqlclient')
+	parse_valid_flag(t, '-test')
+	parse_valid_flag(t, 'darwin -framework Cocoa')
+	parse_valid_flag(t, 'freebsd -I/usr/local/include/freetype2')
+	parse_valid_flag(t, 'linux -lglfw')
+	parse_valid_flag(t, 'mingw -mwindows')
+	parse_valid_flag(t, 'solaris -L/opt/local/lib')
+	parse_valid_flag(t, 'windows -lgdi32')
+	assert t.cflags.len == expected_flags.len
+	for f in expected_flags {
+		assert t.has_cflag(f)
+	}
+}
+
+fn test_parse_invalid_cflags() {
+	t := table.new_table()
+	// -I, -L, -l must have values
+	assert_parse_invalid_flag(t, 'windows -l')
+	assert_parse_invalid_flag(t, '-I')
+	assert_parse_invalid_flag(t, '-L')
+	// OS/compiler name only is not allowed
+	assert_parse_invalid_flag(t, 'darwin')
+	assert_parse_invalid_flag(t, 'freebsd')
+	assert_parse_invalid_flag(t, 'linux')
+	assert_parse_invalid_flag(t, 'mingw')
+	assert_parse_invalid_flag(t, 'solaris')
+	assert_parse_invalid_flag(t, 'windows')
+	// Empty flag is not allowed
+	assert_parse_invalid_flag(t, no_flag)
+	assert t.cflags.len == 0
+}
+
+fn parse_valid_flag(t &table.Table, flag string) {
+	t.parse_cflag(flag, module_name, cdefines) or {
+	}
+}
+
+fn assert_parse_invalid_flag(t &table.Table, flag string) {
+	t.parse_cflag(flag, module_name, cdefines) or {
+		return
+	}
+	assert false
+}
+
+fn make_flag(os, name, value string) cflag.CFlag {
+	return cflag.CFlag{
+		mod: module_name
+		os: os
+		name: name
+		value: value
+	}
+}