diff --git a/test/T260-thread-order.sh b/test/T260-thread-order.sh
index 7f71ce09..fea61275 100755
--- a/test/T260-thread-order.sh
+++ b/test/T260-thread-order.sh
@@ -4,7 +4,7 @@ test_description="threading when messages received out of order"
 
 # Generate all single-root four message thread structures.  We'll use
 # this for multiple tests below.
-THREADS=$($NOTMUCH_PYTHON ${TEST_DIRECTORY}/gen-threads.py 4)
+THREADS=$($NOTMUCH_PYTHON ${NOTMUCH_SRCDIR}/test/gen-threads.py 4)
 nthreads=$(wc -l <<< "$THREADS")
 
 test_begin_subtest "Messages with one parent get linked in all delivery orders"