diff --git a/server/src/controllers/analytics_controller.ts b/server/src/controllers/analytics_controller.ts
index 682df96..f6218c3 100644
--- a/server/src/controllers/analytics_controller.ts
+++ b/server/src/controllers/analytics_controller.ts
@@ -458,6 +458,7 @@ export async function updateThreshold(
 export async function runLearningWithDetection(id: AnalyticUnit.AnalyticUnitId) {
   // TODO: move setting status somehow "inside" learning
   await AnalyticUnit.setStatus(id, AnalyticUnit.AnalyticUnitStatus.PENDING);
+  await Detection.clearSpans(id);
   runLearning(id)
     .then(() => runDetect(id))
     .catch(err => console.error(err));
diff --git a/server/src/models/detection_model.ts b/server/src/models/detection_model.ts
index 27f786a..e52a869 100644
--- a/server/src/models/detection_model.ts
+++ b/server/src/models/detection_model.ts
@@ -138,3 +138,7 @@ export function getSpanBorders(spans: DetectionSpan[]): number[] {
 
   return spanBorders;
 }
+
+export function clearSpans(analyticUnitId: AnalyticUnitId) {
+  return db.removeMany({ analyticUnitId });
+}