diff --git a/src/data.c b/src/data.c
index b81d1b88545..d38dc5e0c58 100644
--- a/src/data.c
+++ b/src/data.c
@@ -2092,7 +2092,7 @@ or a byte-code object.  IDX starts at 0.  */)
     }
   else
     {
-      int size = 0;
+      ptrdiff_t size = 0;
       if (VECTORP (array))
 	size = ASIZE (array);
       else if (COMPILEDP (array))