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 35057)
+++ /applications/editors/josm/plugins/http2/src/org/openstreetmap/josm/plugins/http2/Http2Client.java	(revision 35058)
@@ -15,4 +15,5 @@
 import java.time.Duration;
 import java.time.LocalDateTime;
+import java.time.ZoneOffset;
 import java.time.format.DateTimeFormatter;
 import java.time.temporal.ChronoField;
@@ -57,5 +58,5 @@
         if (getIfModifiedSince() > 0) {
             requestBuilder.header("If-Modified-Since", DateTimeFormatter.RFC_1123_DATE_TIME.format(
-                    LocalDateTime.ofEpochSecond(getIfModifiedSince(), 0, null)));
+                    LocalDateTime.ofEpochSecond(getIfModifiedSince(), 0, ZoneOffset.UTC)));
         }
         if (!isUseCache()) {