diff --git a/src/main/java/org/forkalsrud/album/web/AlbumServlet.java b/src/main/java/org/forkalsrud/album/web/AlbumServlet.java
index a9fd4e8..6ce401c 100644
--- a/src/main/java/org/forkalsrud/album/web/AlbumServlet.java
+++ b/src/main/java/org/forkalsrud/album/web/AlbumServlet.java
@@ -238,14 +238,14 @@ public class AlbumServlet
 
         if (notModified(req, file)) {
             res.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
-            res.setDateHeader("Expires", System.currentTimeMillis() + (30 * 24 * 3600 * 1000)); // 30 days
+            res.setDateHeader("Expires", System.currentTimeMillis() + (30 * 24 * 3600 * 1000L)); // 30 days
             System.out.println(file.getName() + " not modified (based on date)");
             return;
         }
         String fileEtag = thumbnail.getEtag() + "-" + size;
         if (etagMatches(req, fileEtag)) {
             res.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
-            res.setDateHeader("Expires", System.currentTimeMillis() + (30 * 24 * 3600 * 1000)); // 30 days
+            res.setDateHeader("Expires", System.currentTimeMillis() + (30 * 24 * 3600 * 1000L)); // 30 days
             System.out.println(file.getName() + " not modified (based on etag)");
             return;
         }
@@ -269,7 +269,7 @@ public class AlbumServlet
         res.setStatus(HttpServletResponse.SC_OK);
         res.setDateHeader("Last-Modified", file.lastModified());
         res.setHeader("ETag", fileEtag);
-        res.setDateHeader("Expires", System.currentTimeMillis() + (30 * 24 * 3600 * 1000)); // 30 days
+        res.setDateHeader("Expires", System.currentTimeMillis() + (30 * 24 * 3600 * 1000L)); // 30 days
         res.setContentType(cimg.mimeType);
         res.setContentLength(cimg.bits.length);
         res.getOutputStream().write(cimg.bits);