diff --git a/changelog_unreleased/api/15123.md b/changelog_unreleased/api/15123.md
new file mode 100644
index 000000000..27646c626
--- /dev/null
+++ b/changelog_unreleased/api/15123.md
@@ -0,0 +1,10 @@
+#### Add missing type definition for `printer.preprocess` (#15123 by @so1ve)
+
+```diff
+export interface Printer<T = any> {
+  // ...
++ preprocess?:
++   | ((ast: T, options: ParserOptions<T>) => T | Promise<T>)
++   | undefined;
+}
+```
diff --git a/src/index.d.ts b/src/index.d.ts
index c4a160ca2..4200e7ba4 100644
--- a/src/index.d.ts
+++ b/src/index.d.ts
@@ -485,6 +485,9 @@ export interface Printer<T = any> {
         | Doc
         | null)
     | undefined;
+  preprocess?:
+    | ((ast: T, options: ParserOptions<T>) => T | Promise<T>)
+    | undefined;
   insertPragma?: (text: string) => string;
   /**
    * @returns `null` if you want to remove this node