diff --git a/mod/book/deprecatedlib.php b/mod/book/deprecatedlib.php
index 8c2c23ec10e..6783da2d6bd 100644
--- a/mod/book/deprecatedlib.php
+++ b/mod/book/deprecatedlib.php
@@ -36,3 +36,16 @@ function book_scale_used() {
 function book_get_nav_types() {
     throw new coding_exception(__FUNCTION__ . '() has been removed.');
 }
+
+/**
+ * Returns list of available navigation link CSS classes.
+ *
+ * @deprecated since Moodle 4.4.
+ * @todo MDL-81328 Final deprecation in Moodle 4.8.
+ * @return array
+ */
+function book_get_nav_classes() {
+    debugging(__FUNCTION__ . '() is deprecated. There is no replacement.');
+
+    return ['navtoc', 'navimages', 'navtext'];
+}
diff --git a/mod/book/lib.php b/mod/book/lib.php
index 4ad547c73a3..32254d72ed5 100644
--- a/mod/book/lib.php
+++ b/mod/book/lib.php
@@ -43,14 +43,6 @@ function book_get_numbering_types() {
     );
 }
 
-/**
- * Returns list of available navigation link CSS classes.
- * @return array
- */
-function book_get_nav_classes() {
-    return array ('navtoc', 'navimages', 'navtext');
-}
-
 /**
  * Add book instance.
  *
diff --git a/mod/book/upgrade.txt b/mod/book/upgrade.txt
index dce1213b606..d3c9de423c6 100644
--- a/mod/book/upgrade.txt
+++ b/mod/book/upgrade.txt
@@ -1,8 +1,10 @@
-This files describes API changes in the book code.
+This file describes API changes in the book code.
 
 === 4.4 ===
 
 * The previously deprecated `book_get_nav_types` method has been removed, along with the `BOOK_LINK_*` constants
+* book_get_nav_classes() has been deprecated and won't have replacement because it's not required anymore. It should have been
+  deprecated together with book_get_nav_types.
 
 === 4.0 ===