diff --git a/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java b/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java
index 279ca23..b2e32c6 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java
@@ -86,6 +86,7 @@ public enum Quarter implements IWithIntCode {
      */
     @StaticFactoryMethod(Quarter.class)
     public static Quarter fromMonth(Month month) {
+        AssertTools.checkNotNull(month);
         final int monthValue = month.getValue();
         return of(computeQuarterValueInternal(monthValue));
     }