diff --git a/src/ostree/ot-builtin-prune.c b/src/ostree/ot-builtin-prune.c
index 73dfe5e5da..0b4e8698a6 100644
--- a/src/ostree/ot-builtin-prune.c
+++ b/src/ostree/ot-builtin-prune.c
@@ -208,6 +208,15 @@ ostree_builtin_prune (int argc, char **argv, OstreeCommandInvocation *invocation
     }
   else
     {
+      /* In this branch, we need to compute the reachability set manually.
+       * While we do this, we can't let new content in since it'll race with
+       * reachability calculations and we may immediately nuke it. So push an
+       * exclusive lock now. */
+      g_autoptr(OstreeRepoAutoLock) lock =
+        ostree_repo_auto_lock_push (repo, OSTREE_REPO_LOCK_EXCLUSIVE, cancellable, error);
+      if (!lock)
+        return FALSE;
+
       g_autoptr(GHashTable) all_refs = NULL;
       g_autoptr(GHashTable) reachable = ostree_repo_traverse_new_reachable ();
       g_autoptr(GHashTable) retain_branch_depth = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
diff --git a/tests/test-prune.sh b/tests/test-prune.sh
index bbb77a23de..0e628405d5 100755
--- a/tests/test-prune.sh
+++ b/tests/test-prune.sh
@@ -363,4 +363,16 @@ ${CMD_PREFIX} ostree --repo=repo prune --commit-only --keep-younger-than="1 week
 assert_repo_has_n_commits repo 4
 assert_repo_has_n_non_commit_objects repo ${orig_obj_count}
 tap_ok --commit-only and --keep-younger-than
+
+reinitialize_commit_only_test_repo
+for i in {1..10}; do
+    ${CMD_PREFIX} ostree --repo=repo prune --commit-only --keep-younger-than="1 week ago" &
+    commit=$(${CMD_PREFIX} ostree --repo=repo commit --branch foobar tree)
+    wait $!
+    if ! ostree show --repo=repo ${commit}; then
+        assert_not_reached "commit ${commit} on branch foobar was pruned?"
+    fi
+done
+tap_ok commit and prune together
+
 tap_end