1 files changed, 3 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 0a7c6d8ac4..f33ba87435 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -467,6 +467,7 @@ module ActiveRecord
         UNIQUE_VIOLATION      = "23505"
         SERIALIZATION_FAILURE = "40001"
         DEADLOCK_DETECTED     = "40P01"
+        DUPLICATE_DATABASE    = "42P04"
         LOCK_NOT_AVAILABLE    = "55P03"
         QUERY_CANCELED        = "57014"
 
@@ -488,6 +489,8 @@ module ActiveRecord
             SerializationFailure.new(message, sql: sql, binds: binds)
           when DEADLOCK_DETECTED
             Deadlocked.new(message, sql: sql, binds: binds)
+          when DUPLICATE_DATABASE
+            DatabaseAlreadyExists.new(message, sql: sql, binds: binds)
           when LOCK_NOT_AVAILABLE
             LockWaitTimeout.new(message, sql: sql, binds: binds)
           when QUERY_CANCELED