diff --git a/collects/mzlib/inflate.ss b/collects/mzlib/inflate.ss
index 4580311..0a80975 100644
--- a/collects/mzlib/inflate.ss
+++ b/collects/mzlib/inflate.ss
@@ -246,12 +246,14 @@
   (define (NEEDBITS n)
     (when (< bk n)
       (let ([v (peek-byte input-port peeked)])
-	(unless (eof-object? v)
-	  (set! bb (+ bb (arithmetic-shift v bk)))
-	  ;; assume that lookahead never needs more than 32 bytes:
-	  (if (peeked . < . 32)
-	      (set! peeked (add1 peeked))
-	      (read-byte input-port))))
+	(if (eof-object? v)
+	    (error 'inflate "unexpected end of file")
+	    (begin
+	      (set! bb (+ bb (arithmetic-shift v bk)))
+	      ;; assume that lookahead never needs more than 32 bytes:
+	      (if (peeked . < . 32)
+		  (set! peeked (add1 peeked))
+		  (read-byte input-port)))))
       (set! bk (+ bk 8))
       (NEEDBITS n)))
   (define (DUMPBITS n)