diff --git a/src/runner/QCheck_base_runner.mli b/src/runner/QCheck_base_runner.mli
index 5489a10e..82eefe41 100644
--- a/src/runner/QCheck_base_runner.mli
+++ b/src/runner/QCheck_base_runner.mli
@@ -100,8 +100,14 @@ val run_tests :
 (** Run a suite of tests, and print its results. This is an heritage from
     the "qcheck" library.
     @return an error code, [0] if all tests passed, [1] otherwise.
-    @param colors if true, colorful output
-    @param verbose if true, prints more information about test cases *)
+    @param colors if true (default), colorful output
+    @param verbose if true, prints more information about test cases (default: [false])
+    @param debug_shrink [debug_shrink:(Some ch)] writes a log of successful shrink
+    attempts to channel [ch], for example [~debug_shrink:(Some (open_out "mylog.txt"))].
+    Use together with a non-empty list in [~debug_shrink_list].
+    @param debug_shrink_list the test names to log successful shrink attempts for,
+    for example [~debug_shrink_list:["list_rev_is_involutive"]].
+    Requires [~debug_shrink] to be [Some ch]. *)
 
 val run_tests_main : ?argv:string array -> QCheck2.Test.t list -> 'a
 (** Can be used as the main function of a test file. Exits with a non-0 code