diff --git a/opa-fmgui.changes b/opa-fmgui.changes
index 90f493f..038d3b1 100644
--- a/opa-fmgui.changes
+++ b/opa-fmgui.changes
@@ -1,3 +1,8 @@
+-------------------------------------------------------------------
+Wed Dec 11 07:19:06 UTC 2024 - Bernhard Wiedemann <bwiedemann@suse.com>
+
+- Normalize jar mtimes for reproducible builds (boo#1134568)
+
 -------------------------------------------------------------------
 Mon Feb 26 12:39:04 UTC 2024 - Dominique Leuenberger <dimstar@opensuse.org>
 
diff --git a/opa-fmgui.spec b/opa-fmgui.spec
index 9ae90b8..c2a8afe 100644
--- a/opa-fmgui.spec
+++ b/opa-fmgui.spec
@@ -103,7 +103,11 @@ cp %{_sourcedir}/*.jar lib/
 pushd gritty
 mkdir -p classes
 javac -d classes -source 8 -target 8 -cp %{SOURCE20}:%{SOURCE25} $(find . -name \*.java | xargs)
-jar -cf ../lib/gritty.jar -C classes .
+jar \
+%if %{?pkg_vcmp:%pkg_vcmp java-devel >= 17}%{!?pkg_vcmp:0}
+    --date="$(date -u -d @${SOURCE_DATE_EPOCH:-$(date +%%s)} +%%Y-%%m-%%dT%%H:%%M:%%SZ)" \
+%endif
+  --create --file=../lib/gritty.jar -C classes .
 popd
 
 %{ant}