diff --git a/guix-data-service/model/blocked-builds.scm b/guix-data-service/model/blocked-builds.scm
index 10219df..b6f8d69 100644
--- a/guix-data-service/model/blocked-builds.scm
+++ b/guix-data-service/model/blocked-builds.scm
@@ -61,7 +61,7 @@ WITH RECURSIVE all_derivations(id, file_name) AS (
     INNER JOIN derivations
       ON derivation_inputs.derivation_id = derivations.id
 )
-SELECT builds.derivation_output_details_set_id
+SELECT DISTINCT builds.derivation_output_details_set_id
 FROM all_derivations
 INNER JOIN derivations_by_output_details_set
   ON all_derivations.id = derivations_by_output_details_set.derivation_id