3 files changed, 11 insertions, 9 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 13c08d0b55..07d41b1c18 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Do not allow passing the column name to `count` when a block is passed.
+
+    *Rafael Mendonça França*
+
 *   Remove delegation of missing methods in a relation to arel.
 
     *Rafael Mendonça França*
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index c2c4a5a882..40bae89170 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -41,15 +41,13 @@ module ActiveRecord
     def count(column_name = nil)
       if block_given?
         unless column_name.nil?
-          ActiveSupport::Deprecation.warn \
-            "When `count' is called with a block, it ignores other arguments. " \
-            "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0."
+          raise ArgumentError, "Column name argument is not supported when a block is passed."
         end
 
-        return super()
+        super()
+      else
+        calculate(:count, column_name)
       end
-
-      calculate(:count, column_name)
     end
 
     # Calculates the average value on a given column. Returns +nil+ if there's
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index ade6b9e832..5075fed114 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -917,9 +917,9 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal({ "proposed" => 2, "published" => 2 }, Book.group(:status).count)
   end
 
-  def test_deprecate_count_with_block_and_column_name
-    assert_deprecated do
-      assert_equal 6, Account.count(:firm_id) { true }
+  def test_count_with_block_and_column_name_raises_an_error
+    assert_raises(ArgumentError) do
+      Account.count(:firm_id) { true }
     end
   end