diff --git a/CHANGELOG.md b/CHANGELOG.md
index 36f2aa08..3b07ae4f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Changes
+
+* [#126](https://github.com/rubocop/rubocop-minitest/issues/126): Mark `Minitest/AssertWithExpectedArgument` as unsafe. ([@koic][])
+
 ## 0.11.0 (2021-03-22)
 
 ### New features
diff --git a/config/default.yml b/config/default.yml
index 9ce0b4e6..e5677874 100644
--- a/config/default.yml
+++ b/config/default.yml
@@ -97,6 +97,7 @@ Minitest/AssertTruthy:
 Minitest/AssertWithExpectedArgument:
   Description: 'This cop tries to detect when a user accidentally used `assert` when they meant to use `assert_equal`.'
   Enabled: pending
+  Safe: false
   VersionAdded: '0.11'
 
 Minitest/GlobalExpectations:
diff --git a/docs/modules/ROOT/pages/cops_minitest.adoc b/docs/modules/ROOT/pages/cops_minitest.adoc
index e1f8f1d8..130bd62f 100644
--- a/docs/modules/ROOT/pages/cops_minitest.adoc
+++ b/docs/modules/ROOT/pages/cops_minitest.adoc
@@ -447,7 +447,7 @@ assert(actual, 'message')
 | Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
 
 | Pending
-| Yes
+| No
 | No
 | 0.11
 | -
@@ -456,6 +456,9 @@ assert(actual, 'message')
 This cop tries to detect when a user accidentally used
 `assert` when they meant to use `assert_equal`.
 
+It is marked as unsafe because it is not possible to determine
+whether the second argument of `assert` is a message or not.
+
 === Examples
 
 [source,ruby]
diff --git a/lib/rubocop/cop/minitest/assert_with_expected_argument.rb b/lib/rubocop/cop/minitest/assert_with_expected_argument.rb
index 938b447a..ec5ae247 100644
--- a/lib/rubocop/cop/minitest/assert_with_expected_argument.rb
+++ b/lib/rubocop/cop/minitest/assert_with_expected_argument.rb
@@ -6,6 +6,9 @@ module Minitest
       # This cop tries to detect when a user accidentally used
       # `assert` when they meant to use `assert_equal`.
       #
+      # It is marked as unsafe because it is not possible to determine
+      # whether the second argument of `assert` is a message or not.
+      #
       # @example
       #   # bad
       #   assert(3, my_list.length)