diff --git a/test/runtests.sh b/test/runtests.sh
index ea19f4bf14..6dc03536e0 100755
--- a/test/runtests.sh
+++ b/test/runtests.sh
@@ -82,6 +82,14 @@ else
 	TESTS="$(join , "${ARGS[@]}")"
 fi
 
+# Increase open files limit
+#
+# Mozilla file functions (OS.File.move()/copy(), NetUtil.asyncFetch/asyncCopy()) can leave file
+# descriptors open for a few seconds (even with an explicit inputStream.close() in the case of
+# the latter), so a source installation that copies ~500 translators and styles (with fds for
+# source and target) can exceed the default 1024 limit.
+ulimit -n 5000
+
 # Set up profile directory
 PROFILE="`mktemp -d 2>/dev/null || mktemp -d -t 'zotero-unit'`"
 mkdir "$PROFILE/extensions"