diff --git a/guix-data-service/model/derivation.scm b/guix-data-service/model/derivation.scm
index 05cb9ea..05a94e3 100644
--- a/guix-data-service/model/derivation.scm
+++ b/guix-data-service/model/derivation.scm
@@ -1965,16 +1965,17 @@ SELECT COUNT(DISTINCT derivation_id), COUNT(*) FROM derivation_outputs"))
     (match (exec-query conn query)
       (((derivation_id_count all_count))
 
-       (exec-query
-        conn
-        (format
-         #f
-         "
+       (unless (< (string->number all_count) 1)
+         (exec-query
+          conn
+          (format
+           #f
+           "
 ALTER TABLE derivation_outputs
   ALTER COLUMN derivation_id
   SET (n_distinct = ~7f)"
-         (* -1 (/ (string->number derivation_id_count)
-                  (string->number all_count)))))))))
+           (* -1 (/ (string->number derivation_id_count)
+                    (string->number all_count))))))))))
 
 (define (vacuum-derivation-outputs-table conn)
   (exec-query