diff --git a/src/basic/chase-symlinks.c b/src/basic/chase-symlinks.c
index ad1c92900b..afab54f067 100644
--- a/src/basic/chase-symlinks.c
+++ b/src/basic/chase-symlinks.c
@@ -125,11 +125,12 @@ int chase_symlinks(
          *
          * 4. With CHASE_SAFE: in this case the path must not contain unsafe transitions, i.e. transitions from
          *    unprivileged to privileged files or directories. In such cases the return value is -ENOLINK. If
-         *    CHASE_WARN is also set, a warning describing the unsafe transition is emitted.
+         *    CHASE_WARN is also set, a warning describing the unsafe transition is emitted. CHASE_WARN cannot
+         *    be used in PID 1.
          *
          * 5. With CHASE_NO_AUTOFS: in this case if an autofs mount point is encountered, path normalization
          *    is aborted and -EREMOTE is returned. If CHASE_WARN is also set, a warning showing the path of
-         *    the mount point is emitted.
+         *    the mount point is emitted. CHASE_WARN cannot be used in PID 1.
          */
 
         /* A root directory of "/" or "" is identical to none */
diff --git a/src/basic/chase-symlinks.h b/src/basic/chase-symlinks.h
index 7e45b0cbab..a9ee58f9f7 100644
--- a/src/basic/chase-symlinks.h
+++ b/src/basic/chase-symlinks.h
@@ -15,7 +15,8 @@ typedef enum ChaseSymlinksFlags {
         CHASE_STEP        = 1 << 5, /* Just execute a single step of the normalization */
         CHASE_NOFOLLOW    = 1 << 6, /* Do not follow the path's right-most component. With ret_fd, when the path's
                                      * right-most component refers to symlink, return O_PATH fd of the symlink. */
-        CHASE_WARN        = 1 << 7, /* Emit an appropriate warning when an error is encountered */
+        CHASE_WARN        = 1 << 7, /* Emit an appropriate warning when an error is encountered.
+                                     * Note: this may do an NSS lookup, hence this flag cannot be used in PID 1. */
 } ChaseSymlinksFlags;
 
 bool unsafe_transition(const struct stat *a, const struct stat *b);