diff --git a/tests/golden/large-fragmented-free b/tests/golden/large-fragmented-free
index 58aea5f7..7740849c 100644
--- a/tests/golden/large-fragmented-free
+++ b/tests/golden/large-fragmented-free
@@ -1,3 +1,4 @@
+== setting longer hung task timeout
 == creating fragmented extents
 == unlink file with moved extents to free extents per block
 == cleanup
diff --git a/tests/tests/large-fragmented-free.sh b/tests/tests/large-fragmented-free.sh
index e27d1bbe..33f3bef7 100644
--- a/tests/tests/large-fragmented-free.sh
+++ b/tests/tests/large-fragmented-free.sh
@@ -10,6 +10,30 @@ EXTENTS_PER_BTREE_BLOCK=600
 EXTENTS_PER_LIST_BLOCK=8192
 FREED_EXTENTS=$((EXTENTS_PER_BTREE_BLOCK * EXTENTS_PER_LIST_BLOCK))
 
+#
+# This test specifically creates a pathologically sparse file that will
+# be as expensive as possible to free.  This is usually fine on
+# dedicated or reasonable hardware, but trying to run this in
+# virtualized debug kernels can take a very long time.  This test is
+# about making sure that the server doesn't fail, not that the platform
+# can handle the scale of work that our btree formats happen to require
+# while execution is bogged down with use-after-free memory reference
+# tracking.  So we give the test a lot more breathing room before
+# deciding that its hung.
+#
+echo "== setting longer hung task timeout"
+if [ -w /proc/sys/kernel/hung_task_timeout_secs ]; then
+	secs=$(cat /proc/sys/kernel/hung_task_timeout_secs)
+	test "$secs" -gt 0 || \
+		t_fail "confusing value '$secs' from /proc/sys/kernel/hung_task_timeout_secs"
+	restore_hung_task_timeout()
+	{
+		echo "$secs" > /proc/sys/kernel/hung_task_timeout_secs
+	}
+	trap restore_hung_task_timeout EXIT
+	echo "$((secs * 5))" > /proc/sys/kernel/hung_task_timeout_secs
+fi
+
 echo "== creating fragmented extents"
 fragmented_data_extents $FREED_EXTENTS $EXTENTS_PER_BTREE_BLOCK "$T_D0/alloc" "$T_D0/move"