4 files changed, 23 insertions, 6 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 5d04551125..c91e6662c9 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Using `group` with an attribute that has a custom type will properly cast
+    the hash keys after calling a calculation method like `count`. Fixes #25595.
+
+    *Sean Griffin*
+
 *   Fix the generated `#to_param` method to use `omission: ''` so that
     the resulting output is actually up to 20 characters, not
     effectively 17 to leave room for the default "...".
diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index 7996c32bbc..114686c5d3 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -282,8 +282,12 @@ module ActiveRecord
       #
       # +attr_name+ The name of the attribute to retrieve the type for. Must be
       # a string
-      def type_for_attribute(attr_name)
-        attribute_types[attr_name]
+      def type_for_attribute(attr_name, &block)
+        if block
+          attribute_types.fetch(attr_name, &block)
+        else
+          attribute_types[attr_name]
+        end
       end
 
       # Returns a hash where the keys are column names and the values are
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index d6d92b8607..a97b71815a 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -312,8 +312,10 @@ module ActiveRecord
 
       Hash[calculated_data.map do |row|
         key = group_columns.map { |aliaz, col_name|
-          column = calculated_data.column_types.fetch(aliaz) do
-            type_for(col_name)
+          column = type_for(col_name) do
+            calculated_data.column_types.fetch(aliaz) do
+              Type::Value.new
+            end
           end
           type_cast_calculated_value(row[aliaz], column)
         }
@@ -346,9 +348,9 @@ module ActiveRecord
       @klass.connection.table_alias_for(table_name)
     end
 
-    def type_for(field)
+    def type_for(field, &block)
       field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split('.').last
-      @klass.type_for_attribute(field_name)
+      @klass.type_for_attribute(field_name, &block)
     end
 
     def type_cast_calculated_value(value, type, operation = nil)
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index cfae700159..06c2f10dc6 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require "models/book"
 require 'models/club'
 require 'models/company'
 require "models/contract"
@@ -793,4 +794,9 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 50, result[1].credit_limit
     assert_equal 50, result[2].credit_limit
   end
+
+  def test_group_by_attribute_with_custom_type
+    Book.create!(status: :published)
+    assert_equal({ "published" => 1 }, Book.group(:status).count)
+  end
 end