diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
index 526aa20b2c0a5e8862bec1a894dd8c5b606e21a2..22abdee4b8e819f9542e658ad45ee3091e4c847e 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
@@ -64,7 +64,7 @@ def visit_PrimaryKeyDefinition(o)
           end
 
           def visit_ForeignKeyDefinition(o)
-            sql = <<~SQL
+            sql = +<<~SQL
               CONSTRAINT #{quote_column_name(o.name)}
               FOREIGN KEY (#{quote_column_name(o.column)})
                 REFERENCES #{quote_table_name(o.to_table)} (#{quote_column_name(o.primary_key)})