diff --git a/core/kernel.rbs b/core/kernel.rbs
index fac5a887d..be48950a6 100644
--- a/core/kernel.rbs
+++ b/core/kernel.rbs
@@ -183,8 +183,8 @@ module Kernel : BasicObject
   #     c(5)   #=> nil
   #
   def self?.caller: () -> Array[String]
-                  | (int start, ?int? length) -> Array[String]?
-                  | (range[int] range) -> Array[String]?
+                  | %a{implicitly-returns-nil} (int start, ?int? length) -> Array[String]
+                  | %a{implicitly-returns-nil} (range[int] range) -> Array[String]
 
   # <!--
   #   rdoc-file=vm_backtrace.c
@@ -208,8 +208,8 @@ module Kernel : BasicObject
   # entries within the specified range.
   #
   def self?.caller_locations: () -> Array[Thread::Backtrace::Location]
-                            | (int start, ?int? length) -> Array[Thread::Backtrace::Location]?
-                            | (range[int] range) -> Array[Thread::Backtrace::Location]?
+                            | %a{implicitly-returns-nil} (int start, ?int? length) -> Array[Thread::Backtrace::Location]
+                            | %a{implicitly-returns-nil} (range[int] range) -> Array[Thread::Backtrace::Location]
 
   # <!--
   #   rdoc-file=vm_eval.c