-(defvar *eql-specializer-methods* (make-hash-table :test 'eql))
-(defvar *class-eq-specializer-methods* (make-hash-table :test 'eq))
+;;;
+;;; These tables are shared between threads, so they need to be synchronized.
+(defvar *eql-specializer-methods* (make-hash-table :test 'eql :synchronized t))
+(defvar *class-eq-specializer-methods* (make-hash-table :test 'eq :synchronized t))