diff --git a/app/models/stream_events.rb b/app/models/stream_events.rb
index e8c5a28..8ba995c 100644
--- a/app/models/stream_events.rb
+++ b/app/models/stream_events.rb
@@ -30,12 +30,12 @@ def self.user_group_ids?(event_data)
 
   def self.started_at(event_data)
     started_at = event_data.fetch('metadata')&.fetch('started_at', nil)
-    Time.parse(started_at) if started_at
+    Time.parse(started_at) rescue nil if started_at
   end
 
   def self.finished_at(event_data)
     finished_at = event_data.fetch('metadata')&.fetch('finished_at', nil)
-    Time.parse(finished_at) if finished_at
+    Time.parse(finished_at) rescue nil if finished_at
   end
 
   def self.session_time(event_data)
diff --git a/spec/models/stream_events_spec.rb b/spec/models/stream_events_spec.rb
index 6ff841f..c3fd16b 100644
--- a/spec/models/stream_events_spec.rb
+++ b/spec/models/stream_events_spec.rb
@@ -51,11 +51,22 @@
       expect(StreamEvents.started_at(event_data)).to be_nil
     end
 
+    it 'returns started_at to nil if started_at cannot be parsed' do
+      # set started_at to some unparseable time string
+      event_metadata['started_at'] = '-1 OR 2+742-742-1=0+0+0+1 --'
+      expect(StreamEvents.started_at(event_data)).to be_nil
+    end
+
     it 'returns finished_at to nil if no finished_at in metadata' do
       event_metadata.delete('finished_at')
       expect(StreamEvents.finished_at(event_data)).to be_nil
     end
 
+    it 'returns finished_at to nil if started_at cannot be parsed' do
+      event_metadata['finished_at'] = '-1 OR 2+742-742-1=0+0+0+1 --'
+      expect(StreamEvents.finished_at(event_data)).to be_nil
+    end
+
     context 'user_group_ids?' do
       it 'returns true if classification done by user that belongs to multiple user groups' do
         expect(StreamEvents.user_group_ids?(event_data)).to be true