diff --git a/Gemfile b/Gemfile
index bb94df82..95a1c679 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,3 +2,6 @@
 
 source "https://rubygems.org"
 gemspec
+
+# minitest 6.0 removed run_one_method which minitest-fork_executor depends on
+gem "minitest", "~> 5.0"
diff --git a/README.md b/README.md
index 7cc55885..14154b69 100644
--- a/README.md
+++ b/README.md
@@ -184,6 +184,16 @@ ActiveRecordDoctor.configure do
 end
 ```
 
+### Multiple Databases
+
+`active_record_doctor` currently only analyzes models connected to the primary
+database. Models that use a different database connection — whether via
+`establish_connection`, `connects_to`, or by inheriting from an abstract class
+with its own connection — are automatically skipped by all detectors.
+
+This means that if you have gems or parts of your application that connect to a
+secondary database, their models won't be checked and won't cause errors.
+
 ### Indexing Unindexed Foreign Keys
 
 Foreign keys should be indexed unless it's proven ineffective. However, Rails
diff --git a/lib/active_record_doctor/detectors/base.rb b/lib/active_record_doctor/detectors/base.rb
index b02630ba..df253d2e 100644
--- a/lib/active_record_doctor/detectors/base.rb
+++ b/lib/active_record_doctor/detectors/base.rb
@@ -156,7 +156,10 @@ def check_constraints(table_name)
       end
 
       def models
-        ActiveRecord::Base.descendants.sort_by(&:name)
+        base_pool = ActiveRecord::Base.connection_pool
+        ActiveRecord::Base.descendants
+          .reject { |model| model.connection_pool != base_pool }
+          .sort_by(&:name)
       end
 
       def underscored_name
diff --git a/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb b/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb
index 675a017f..c1977ffc 100644
--- a/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb
+++ b/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb
@@ -349,4 +349,17 @@ def test_created_on_updated_on_with_null_are_disallowed
       add `NOT NULL` to users.updated_on - timestamp columns are set automatically by Active Record and allowing NULL may lead to inconsistencies introduced by bulk operations
     OUTPUT
   end
+
+  def test_models_with_non_primary_connection_are_skipped
+    # Models connected to a secondary database should be silently skipped.
+    # Previously this would crash with e.g. PG::UndefinedTable when the
+    # secondary table didn't exist in the primary database (see #149).
+    SecondaryContext.create_table(:users) do |t|
+      t.string :name, null: true
+    end.define_model do
+      validates :name, presence: true
+    end
+
+    refute_problems
+  end
 end
diff --git a/test/active_record_doctor/detectors/undefined_table_references_test.rb b/test/active_record_doctor/detectors/undefined_table_references_test.rb
index 4176e089..e4553c06 100644
--- a/test/active_record_doctor/detectors/undefined_table_references_test.rb
+++ b/test/active_record_doctor/detectors/undefined_table_references_test.rb
@@ -52,4 +52,12 @@ def test_global_ignore_tables
 
     refute_problems
   end
+
+  def test_models_with_non_primary_connection_are_skipped
+    # Models connected to a secondary database should be silently skipped,
+    # not reported as referencing undefined tables (see #149).
+    SecondaryContext.create_table(:users).define_model
+
+    refute_problems
+  end
 end
diff --git a/test/setup.rb b/test/setup.rb
index 6be93235..f9445421 100644
--- a/test/setup.rb
+++ b/test/setup.rb
@@ -8,9 +8,11 @@
 
 require "logger"
 require "active_record"
-require "pg"
-require "mysql2"
-require "sqlite3"
+%w[pg mysql2 sqlite3].each do |adapter_gem|
+  require adapter_gem
+rescue LoadError
+  # Not all adapters need to be installed; only the one matching DATABASE_ADAPTER is required.
+end
 
 adapter = ENV.fetch("DATABASE_ADAPTER")
 
@@ -91,6 +93,8 @@ class SecondaryRecord < ApplicationRecord
 
 SecondaryRecord.establish_connection :secondary
 
+SecondaryContext = TransientRecord.context_for SecondaryRecord
+
 if ActiveRecord.version >= Gem::Version.new("7.1")
   # See https://github.com/rails/rails/pull/46522 for details.
   # When `false` (default in Rails 7.1) - validate presence only when the foreign key changed.