diff --git a/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidator.java b/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidator.java
index 7cd01933e5..e8f236c707 100644
--- a/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidator.java
+++ b/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidator.java
@@ -25,6 +25,7 @@ public PickupBookingRuleIdValidator(
   public void validate(GtfsStopTime entity, NoticeContainer noticeContainer) {
     if (entity.hasPickupType()
         && entity.pickupType() == GtfsPickupDropOff.MUST_PHONE
+        && entity.hasStartPickupDropOffWindow()
         && !entity.hasPickupBookingRuleId()) {
       noticeContainer.addValidationNotice(
           new MissingPickupDropOffBookingRuleIdNotice(
@@ -34,6 +35,7 @@ public void validate(GtfsStopTime entity, NoticeContainer noticeContainer) {
     }
     if (entity.hasDropOffType()
         && entity.dropOffType() == GtfsPickupDropOff.MUST_PHONE
+        && entity.hasEndPickupDropOffWindow()
         && !entity.hasDropOffBookingRuleId()) {
       noticeContainer.addValidationNotice(
           new MissingPickupDropOffBookingRuleIdNotice(
@@ -61,8 +63,12 @@ public boolean shouldCallValidate() {
   }
 
   /**
-   * `pickup_booking_rule_id` is recommended when `pickup_type=2` and `drop_off_booking_rule_id` is
-   * recommended when `drop_off_type=2`
+   * pickup_booking_rule_id is recommended when pickup_type=2 and drop_off_booking_rule_id is
+   * recommended when drop_off_type=2.
+   *
+   * <p>Currently, this notice is only triggered on feeds when either start_pickup_drop_off_window
+   * or end_pickup_drop_off_window is defined, since this recommendation was added to the
+   * specification for feeds with GTFS-Flex.
    */
   @GtfsValidationNotice(
       severity = SeverityLevel.WARNING,
diff --git a/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidatorTest.java b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidatorTest.java
index 9735e2a405..4597a716be 100644
--- a/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidatorTest.java
+++ b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/PickupBookingRuleIdValidatorTest.java
@@ -10,6 +10,7 @@
 import org.mobilitydata.gtfsvalidator.notice.ValidationNotice;
 import org.mobilitydata.gtfsvalidator.table.GtfsPickupDropOff;
 import org.mobilitydata.gtfsvalidator.table.GtfsStopTime;
+import org.mobilitydata.gtfsvalidator.type.GtfsTime;
 
 @RunWith(JUnit4.class)
 public class PickupBookingRuleIdValidatorTest {
@@ -27,6 +28,7 @@ public void missingBookingRuleIdShouldGenerateNotice() {
         new GtfsStopTime.Builder()
             .setCsvRowNumber(1)
             .setPickupType(GtfsPickupDropOff.MUST_PHONE)
+            .setStartPickupDropOffWindow(GtfsTime.fromSecondsSinceMidnight(18614))
             .build();
     assertThat(generateNotices(stopTime))
         .containsExactly(
@@ -40,7 +42,8 @@ public void existingBookingRuleIdShouldNotGenerateNotice() {
         new GtfsStopTime.Builder()
             .setCsvRowNumber(2)
             .setPickupType(GtfsPickupDropOff.MUST_PHONE)
-            .setPickupBookingRuleId("bookingRuleId")
+            .setStartPickupDropOffWindow(GtfsTime.fromSecondsSinceMidnight(18614))
+            .setPickupBookingRuleId("booking_rule_id")
             .build();
     assertThat(generateNotices(stopTime)).isEmpty();
   }