diff --git a/get_source.sh b/get_source.sh
index 523487b..7d70291 100755
--- a/get_source.sh
+++ b/get_source.sh
@@ -45,7 +45,18 @@ then
 	echo 'ERROR: did not properly remove problematic content' 1>&2
 	exit 1
 fi
-tar -cv "${TARDIR}/" | zstdmt --ultra -22 > "${NEWTAR}"
+# https://www.gnu.org/software/tar/manual/html_section/Reproducibility.html
+# We discard mtimes entirely, since git doesn’t store per-file mtimes.
+TZ=UTC LC_ALL=C tar \
+    --create --verbose \
+    --sort=name \
+    --format=posix \
+    --numeric-owner --owner=0 --group=0 \
+    --mode=go+u,go-w \
+    --pax-option='delete=atime,delete=ctime' \
+    --clamp-mtime --mtime='@0' \
+    "${TARDIR}/" |
+  zstdmt --ultra -22 > "${NEWTAR}"
 
 cd "${SAVEDIR}"
 mv -v "${XDIR}/${NEWTAR}" .
diff --git a/sources b/sources
index 8717c5c..e2cc213 100644
--- a/sources
+++ b/sources
@@ -1 +1 @@
-SHA512 (pdfminer.six-20231228-filtered.tar.zst) = 1324a38207a3b9926bb43f6665254e848765bdda8587194f2c6ca70f50452d7fc1cf0b57252bda10921f24bc7d48d460bda916b0df5519f4dd3831e2779e1c62
+SHA512 (pdfminer.six-20231228-filtered.tar.zst) = 50d57bb8919684a4479530b6300f4f20acfd8af019e5199f4a70d1afab398c8ff565e8a2137881b331c9feb8c6aaabfe061a4985db34bdd868769d3111ac450f