B737NG flight crew reported rejecting takeoff due to a master caution and door warning.

Attributes
ACN	1459733
Time
Date	201706
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Takeoff
Flight Plan	IFR
Component
Aircraft Component	Exterior Pax/Crew Door
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 267
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 261
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Flight Deck / Cabin / Aircraft Event Other / Unknown

Narrative:

We were cleared for takeoff runway 06. First officer was flying. We had just gotten takeoff power set and a master caution (doors aft entry) light illuminated. We rejected takeoff at 57 knots. We notified tower and advised the passengers. We turned off at F2; cleared the runway; and the door light extinguished. I called the flight attendants (flight attendant) and the c-fa informed me that she saw the door handle not in the horizontal detent; and put it in the closed position as we exited runway. We advised control tower we needed to stop aircraft. We called dispatch desk; and he put me on hold to confer with personnel. He got back to me to insure it was low speed reject and I said yes 57 knots. Dispatcher said we were good to depart. I then had him amend our min takeoff fuel to 18.5.

Original NASA ASRS Text

Title: B737NG flight crew reported rejecting takeoff due to a master caution and door warning.

Narrative: We were cleared for takeoff Runway 06. First Officer was flying. We had just gotten takeoff power set and a Master Caution (doors aft entry) light illuminated. We rejected takeoff at 57 knots. We notified Tower and advised the Passengers. We turned off at F2; cleared the runway; and the door light extinguished. I called the Flight Attendants (FA) and the C-FA informed me that she saw the door handle not in the horizontal detent; and put it in the closed position as we exited runway. We advised Control Tower we needed to stop aircraft. We called Dispatch Desk; and he put me on hold to confer with personnel. He got back to me to insure it was low speed reject and I said yes 57 knots. Dispatcher said we were good to depart. I then had him amend our min takeoff fuel to 18.5.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.