diff --git a/src/man/mkman.sh b/src/man/mkman.sh
index 00c4ffe720f..65a31b2e513 100755
--- a/src/man/mkman.sh
+++ b/src/man/mkman.sh
@@ -5,8 +5,15 @@
 
 set -e
 
-MONTH="$(LC_ALL=C date -u --date="@${SOURCE_DATE_EPOCH:-$(date +%s)}" +%b)"
-YEAR="$(LC_ALL=C date -u --date="@${SOURCE_DATE_EPOCH:-$(date +%s)}" +%Y)"
+test -z "$SOURCE_DATE_EPOCH" && SOURCE_DATE_EPOCH="$(date +%s)"
+
+if LC_ALL=C date -d "@$SOURCE_DATE_EPOCH" >/dev/null 2>/dev/null; then
+	MONTH="$(LC_ALL=C date -u -d "@$SOURCE_DATE_EPOCH" +%b)"
+	YEAR="$(LC_ALL=C date -u -d "@$SOURCE_DATE_EPOCH" +%Y)"
+else
+	MONTH="$(LC_ALL=C date -u +%b)"
+	YEAR="$(LC_ALL=C date -u +%Y)"
+fi
 
 sed \
   -e "s/VERSION/$1/g" \