Index: /applications/editors/josm/plugins/http2/src/org/openstreetmap/josm/plugins/http2/Http2Client.java
===================================================================
--- /applications/editors/josm/plugins/http2/src/org/openstreetmap/josm/plugins/http2/Http2Client.java	(revision 35058)
+++ /applications/editors/josm/plugins/http2/src/org/openstreetmap/josm/plugins/http2/Http2Client.java	(revision 35059)
@@ -58,5 +58,5 @@
         if (getIfModifiedSince() > 0) {
             requestBuilder.header("If-Modified-Since", DateTimeFormatter.RFC_1123_DATE_TIME.format(
-                    LocalDateTime.ofEpochSecond(getIfModifiedSince(), 0, ZoneOffset.UTC)));
+                    LocalDateTime.ofEpochSecond(getIfModifiedSince() / 1000, 0, ZoneOffset.UTC)));
         }
         if (!isUseCache()) {