diff --git a/lib/Db/AbstractResult.php b/lib/Db/AbstractResult.php
index fe4df26..6086cf6 100644
--- a/lib/Db/AbstractResult.php
+++ b/lib/Db/AbstractResult.php
@@ -36,9 +36,9 @@ abstract class AbstractResult implements Result {
         return iterator_to_array($this, false);
     }
 
-    abstract public function changes();
+    abstract public function changes(): int;
 
-    abstract public function lastId();
+    abstract public function lastId(): int;
 
     // PHP iterator methods
 
diff --git a/tests/lib/Result.php b/tests/lib/Result.php
index 7381a34..554c50a 100644
--- a/tests/lib/Result.php
+++ b/tests/lib/Result.php
@@ -37,11 +37,11 @@ class Result implements \JKingWeb\Arsse\Db\Result {
         return iterator_to_array($this, false);
     }
 
-    public function changes() {
+    public function changes(): int {
         return $this->rows;
     }
 
-    public function lastId() {
+    public function lastId(): int {
         return $this->id;
     }