diff --git a/core/nwb.ecephys.yaml b/core/nwb.ecephys.yaml
index 2546aef1..4cd0db67 100644
--- a/core/nwb.ecephys.yaml
+++ b/core/nwb.ecephys.yaml
@@ -104,6 +104,7 @@ groups:
       common experiment master-clock stored in NWBFile.timestamps_reference_time.
       Timestamps are required for the events. Unlike for TimeSeries, timestamps are
       required for SpikeEventSeries and are thus re-specified here.
+    quantity: 1
     attributes:
     - name: interval
       dtype: int32
diff --git a/docs/format/source/format_release_notes.rst b/docs/format/source/format_release_notes.rst
index 3e72748c..542763ed 100644
--- a/docs/format/source/format_release_notes.rst
+++ b/docs/format/source/format_release_notes.rst
@@ -12,6 +12,7 @@ Major changes
   can inherit from it. The second to store external images (#604, #623, #627)
 - Changed ``NWBFile.electrodes`` from a generic ``DynamicTable`` with added columns to a new ``ElectrodesTable`` 
   neurodata type that extends ``DynamicTable`` with added columns. (#539, #624)
+- Made ``SpikeEventSeries.timestamps`` explicitly required as described in the documentation. (#629)
 - Changed ``DecompositionSeries.bands`` from a generic ``DynamicTable`` with added columns to a new ``FrequencyBandsTable`` neurodata type that extends ``DynamicTable`` with added columns. (#610)
 - Allowed `EventDetection` to have shape (num_events, 2) to store the channel index of the detected event. (#620)