diff --git a/cont.c b/cont.c
index 0c49d34742..7f971a9e9d 100644
--- a/cont.c
+++ b/cont.c
@@ -324,6 +324,7 @@ fiber_pool_vacancy_push(struct fiber_pool_vacancy * vacancy, struct fiber_pool_v
 #ifdef FIBER_POOL_ALLOCATION_FREE
     if (head) {
         head->previous = vacancy;
+        vacancy->previous = NULL;
     }
 #endif
 
diff --git a/version.h b/version.h
index c10798ff99..9e8f82a10e 100644
--- a/version.h
+++ b/version.h
@@ -2,7 +2,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 3
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 173
+#define RUBY_PATCHLEVEL 174
 
 #define RUBY_RELEASE_YEAR 2021
 #define RUBY_RELEASE_MONTH 3