diff --git a/server/traces/trace_entities.go b/server/traces/trace_entities.go
index 983fb65b71..7de54e9766 100644
--- a/server/traces/trace_entities.go
+++ b/server/traces/trace_entities.go
@@ -194,6 +194,11 @@ func (t *Trace) Spans() []Span {
 		return []Span{}
 	}
 
+	if len(t.Flat) == 0 {
+		t.Flat = make(map[trace.SpanID]*Span)
+		flattenSpans(t.Flat, t.RootSpan)
+	}
+
 	spans := make([]Span, 0, len(t.Flat))
 	for _, span := range t.Flat {
 		spans = append(spans, *span)