INIT-SELF-SEED: invalid index

[phoe]

SBCL 2.2.9 on debian sid amd64, cl-isaac downloaded from current quicklisp dist.

CL-USER> (ql:quickload :cl-isaac)
To load "cl-isaac":
  Load 1 ASDF system:
    cl-isaac
; Loading "cl-isaac"

(:CL-ISAAC)
CL-USER> (isaac:init-self-seed :is64 t)

Invalid index 23781 for (SIMPLE-ARRAY (UNSIGNED-BYTE 64) (256)), should be a non-negative integer below 256.
   [Condition of type SB-INT:INVALID-ARRAY-INDEX-ERROR]

Restarts:
 0: [RETRY] Retry SLIME REPL evaluation request.
 1: [*ABORT] Return to SLIME's top level.
 2: [ABORT] abort thread (#<THREAD "repl-thread" RUNNING {10013E0143}>)

Backtrace:
  0: (CL-ISAAC:GENERATE-NEXT-ISAAC64-BLOCK #S(CL-ISAAC:ISAAC64-CTX :RANDCNT 0 :RANDRSL #(3934848528393097412 3139001632129883341 14599601752695088836 3102163498744780811 8279641599517826203 175449285896896..
      Locals:
        CTX = #S(CL-ISAAC:ISAAC64-CTX ..)
        I = 0
  1: (CL-ISAAC:SCRAMBLE64 #S(CL-ISAAC:ISAAC64-CTX :RANDCNT 0 :RANDRSL #(3934848528393097412 3139001632129883341 14599601752695088836 3102163498744780811 8279641599517826203 17544928589689641459 ...) :RANDM..
      Locals:
        A = 2294595384479959264
        B = 6784294260755478456
        C = 9559064695926442999
        CTX = #S(CL-ISAAC:ISAAC64-CTX ..)
        D = 9657017499224466276
        E = 16082990964643725320
        F = 18313416023109256564
        G = 5022560803070576583
        H = 13024515163114616408
  2: (CL-ISAAC:INIT-KERNEL-SEED :IS64 T)
      Locals:
        #:.DEFAULTING-TEMP. = T
        CTX = #S(CL-ISAAC:ISAAC64-CTX ..)
        IS64 = T
  3: (CL-ISAAC:INIT-SELF-SEED :COUNT 1 :IS64 T)
      Locals:
        #:.DEFAULTING-TEMP. = 1
        #:.DEFAULTING-TEMP.#1 = T
        ARRAY#1 = #(0 0 0 0 0 0 ...)
        COUNT = 1
        CTX = #S(CL-ISAAC:ISAAC64-CTX :RANDCNT 0 :RANDRSL #(0 0 0 0 0 0 ...) :RANDMEM #(0 0 0 0 0 0 ...) :A 0 :B 0 :C 0)
        I = 0
        SB-INT:INDEX = 0
        IS64 = T
        J = 0
        SB-C::Y = 1
  4: (SB-INT:SIMPLE-EVAL-IN-LEXENV (CL-ISAAC:INIT-SELF-SEED :IS64 T) #<NULL-LEXENV>)
  5: (EVAL (CL-ISAAC:INIT-SELF-SEED :IS64 T))
 --more--