diff --git a/wcs/sql.py b/wcs/sql.py
index 5ba8d68e4..75397daaa 100644
--- a/wcs/sql.py
+++ b/wcs/sql.py
@@ -979,21 +979,37 @@ def do_formdef_indexes(formdef, created, conn, cur, concurrently=False):
     existing_indexes = set()
     if not created:
         cur.execute(
-            '''SELECT indexname
-                         FROM pg_indexes
-                        WHERE schemaname = 'public'
-                          AND tablename IN (%s, %s)''',
+            '''SELECT pci.relname, array_length(pi.indkey, 1)
+                FROM pg_index pi
+                JOIN pg_class pci on pci.oid = pi.indexrelid
+                JOIN pg_class pct on pct.oid = pi.indrelid
+                WHERE pci.relnamespace = 'public'::regnamespace
+                    AND pct.relname in (%s, %s)''',
             (table_name, evolutions_table_name),
         )
-        existing_indexes = {x[0] for x in cur.fetchall()}
+        existing_indexes = {x[0]: x[1] for x in cur.fetchall()}
 
     create_index = 'CREATE INDEX'
     if concurrently:
         create_index = 'CREATE INDEX CONCURRENTLY'
 
-    if evolutions_table_name + '_fid' not in existing_indexes:
+    fid_idx = evolutions_table_name + '_fid'
+
+    if fid_idx in existing_indexes and existing_indexes[fid_idx] != 2:
+        # The index was previously (< #67757) on formdata_id only, so
+        # search for it with only one key and recreate it if needed.
+        if concurrently:
+            cur.execute('DROP INDEX CONCURRENTLY %s' % fid_idx)
+        else:
+            cur.execute('DROP INDEX %s' % fid_idx)
         cur.execute(
-            '''%s %s_fid ON %s (formdata_id)''' % (create_index, evolutions_table_name, evolutions_table_name)
+            '''%s %s_fid ON %s (formdata_id, id)'''
+            % (create_index, evolutions_table_name, evolutions_table_name)
+        )
+    elif fid_idx not in existing_indexes:
+        cur.execute(
+            '''%s %s_fid ON %s (formdata_id, id)'''
+            % (create_index, evolutions_table_name, evolutions_table_name)
         )
 
     for attr in ('receipt_time', 'anonymised', 'user_id', 'status'):