diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index 4424eed..8428aa7 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -12,3 +12,4 @@ People who contributed to hypopg:
   * Joel Van Horn
   * Michael Lroll
   * Godwottery
+  * Jan Koßmann
diff --git a/hypopg_index.c b/hypopg_index.c
index a1c31c3..63da080 100644
--- a/hypopg_index.c
+++ b/hypopg_index.c
@@ -1500,7 +1500,7 @@ hypopg_relation_size(PG_FUNCTION_ARGS)
 		}
 	}
 
-	PG_RETURN_INT64(pages * BLCKSZ);
+	PG_RETURN_INT64(pages * 1.0L * BLCKSZ);
 }
 
 /*