diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index abf6373030..c0264df8e1 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   PostgreSQL adapter automatically reloads it's type map when encountering
+    unknown OIDs.
+
+    Fixes #14678.
+
+    *Matthew Draper*, *Yves Senn*
+
 *   Fix insertion of records via `has_many :through` association with scope.
 
     Fixes #3548.
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
index 51ee2829b2..a5fb048b1e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -142,10 +142,7 @@ module ActiveRecord
           fields.each_with_index do |fname, i|
             ftype = result.ftype i
             fmod  = result.fmod i
-            types[fname] = type_map.fetch(ftype, fmod) { |oid, mod|
-              warn "unknown OID: #{fname}(#{oid}) (#{sql})"
-              OID::Identity.new
-            }
+            types[fname] = get_oid_type(ftype, fmod, fname)
           end
 
           ret = ActiveRecord::Result.new(fields, result.values, types)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index 50a73aa666..1229b4851a 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -182,9 +182,7 @@ module ActiveRecord
         def columns(table_name)
           # Limit, precision, and scale are all handled by the superclass.
           column_definitions(table_name).map do |column_name, type, default, notnull, oid, fmod|
-            oid = type_map.fetch(oid.to_i, fmod.to_i) {
-              OID::Identity.new
-            }
+            oid = get_oid_type(oid.to_i, fmod.to_i, column_name)
             PostgreSQLColumn.new(column_name, default, oid, type, notnull == 'f')
           end
         end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 3510e4f3b0..207e1c4fed 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -559,6 +559,17 @@ module ActiveRecord
           @type_map
         end
 
+        def get_oid_type(oid, fmod, column_name)
+          if !type_map.key?(oid)
+            initialize_type_map(type_map, [oid])
+          end
+
+          type_map.fetch(oid, fmod) {
+            warn "unknown OID #{oid}: failed to recognize type of #{column_name}"
+            OID::Identity.new
+          }
+        end
+
         def reload_type_map
           type_map.clear
           initialize_type_map(type_map)
@@ -583,19 +594,25 @@ module ActiveRecord
           type_map
         end
 
-        def initialize_type_map(type_map)
+        def initialize_type_map(type_map, oids = nil)
           if supports_ranges?
-            result = execute(<<-SQL, 'SCHEMA')
+            query = <<-SQL
               SELECT t.oid, t.typname, t.typelem, t.typdelim, t.typinput, r.rngsubtype, t.typtype, t.typbasetype
               FROM pg_type as t
               LEFT JOIN pg_range as r ON oid = rngtypid
             SQL
           else
-            result = execute(<<-SQL, 'SCHEMA')
+            query = <<-SQL
               SELECT t.oid, t.typname, t.typelem, t.typdelim, t.typinput, t.typtype, t.typbasetype
               FROM pg_type as t
             SQL
           end
+
+          if oids
+            query += "WHERE t.oid::integer IN (%s)" % oids.join(", ")
+          end
+
+          result = execute(query, 'SCHEMA')
           ranges, nodes = result.partition { |row| row['typtype'] == 'r' }
           enums, nodes = nodes.partition { |row| row['typtype'] == 'e' }
           domains, nodes = nodes.partition { |row| row['typtype'] == 'd' }
diff --git a/activerecord/test/cases/adapters/postgresql/domain_test.rb b/activerecord/test/cases/adapters/postgresql/domain_test.rb
index 214e89dd7f..5286a847a4 100644
--- a/activerecord/test/cases/adapters/postgresql/domain_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/domain_test.rb
@@ -19,9 +19,6 @@ class PostgresqlDomainTest < ActiveRecord::TestCase
         t.column :price, :custom_money
       end
     end
-
-    # reload type map after creating the enum type
-    @connection.send(:reload_type_map)
   end
 
   teardown do
diff --git a/activerecord/test/cases/adapters/postgresql/enum_test.rb b/activerecord/test/cases/adapters/postgresql/enum_test.rb
index 73da5a74ab..4146b117f6 100644
--- a/activerecord/test/cases/adapters/postgresql/enum_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/enum_test.rb
@@ -21,8 +21,6 @@ class PostgresqlEnumTest < ActiveRecord::TestCase
         t.column :current_mood, :mood
       end
     end
-    # reload type map after creating the enum type
-    @connection.send(:reload_type_map)
   end
 
   teardown do
diff --git a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
index 49d8ec238d..d319bd0b80 100644
--- a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
@@ -1,11 +1,13 @@
 # encoding: utf-8
 require "cases/helper"
 require 'support/ddl_helper'
+require 'support/connection_helper'
 
 module ActiveRecord
   module ConnectionAdapters
     class PostgreSQLAdapterTest < ActiveRecord::TestCase
       include DdlHelper
+      include ConnectionHelper
 
       def setup
         @connection = ActiveRecord::Base.connection
@@ -357,6 +359,32 @@ module ActiveRecord
         end
       end
 
+      def test_reload_type_map_for_newly_defined_types
+        @connection.execute "CREATE TYPE feeling AS ENUM ('good', 'bad')"
+        result = @connection.select_all "SELECT 'good'::feeling"
+        assert_instance_of(PostgreSQLAdapter::OID::Enum,
+                           result.column_types["feeling"])
+      ensure
+        @connection.execute "DROP TYPE IF EXISTS feeling"
+        reset_connection
+      end
+
+      def test_only_reload_type_map_once_for_every_unknown_type
+        silence_warnings do
+          assert_queries 2, ignore_none: true do
+            @connection.select_all "SELECT NULL::anyelement"
+          end
+          assert_queries 1, ignore_none: true do
+            @connection.select_all "SELECT NULL::anyelement"
+          end
+          assert_queries 2, ignore_none: true do
+            @connection.select_all "SELECT NULL::anyarray"
+          end
+        end
+      ensure
+        reset_connection
+      end
+
       private
       def insert(ctx, data)
         binds   = data.map { |name, value|
diff --git a/activerecord/test/cases/adapters/postgresql/range_test.rb b/activerecord/test/cases/adapters/postgresql/range_test.rb
index 57c7da2657..060b17d071 100644
--- a/activerecord/test/cases/adapters/postgresql/range_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/range_test.rb
@@ -34,7 +34,6 @@ _SQL
 
           @connection.add_column 'postgresql_ranges', 'float_range', 'floatrange'
         end
-        @connection.send :reload_type_map
         PostgresqlRange.reset_column_information
       rescue ActiveRecord::StatementInvalid
         skip "do not test on PG without range"