diff --git a/src/vs/base/common/color.ts b/src/vs/base/common/color.ts
index c92127cf5b48337b20cd8fa7e247df4ba5f8200d..6dc7eb65aef2515b5ac3da55a60f77ffdabf036a 100644
--- a/src/vs/base/common/color.ts
+++ b/src/vs/base/common/color.ts
@@ -114,7 +114,7 @@ export class HSLA {
 		return new HSLA(h, s, l, a);
 	}
 
-	private static _hue2rgb(p: number, q: number, t: number) {
+	private static _hue2rgb(p: number, q: number, t: number): number {
 		if (t < 0) {
 			t += 1;
 		}