diff --git a/lib/chibi/io/io.scm b/lib/chibi/io/io.scm
index 13c616f6..36ec8511 100644
--- a/lib/chibi/io/io.scm
+++ b/lib/chibi/io/io.scm
@@ -99,10 +99,10 @@
  ((not string-streams)
   (define (%read-string n in)
     (let ((out (open-output-string)))
-      (do ((i 0 (+ i 1))
-           (ch (read-char in) (read-char in)))
-          ((or (= i n) (eof-object? ch)) (list i (get-output-string out)))
-        (write-char ch out))))))
+      (let lp ((i 0))
+        (cond ((or (= i n) (eof-object? (peek-char in)))
+               (list i (get-output-string out)))
+              (else (write-char (read-char in) out) (lp (+ i 1)))))))))
 
 (define (read-string n . o)
   (if (zero? n)
@@ -129,13 +129,12 @@
 (cond-expand
  ((not string-streams)
   (define (%read-string! str n in)
-    (do ((i 0 (+ i 1))
-         (ch (read-char in) (read-char in)))
-        ((or (= i n) (eof-object? ch)) i)
-      (string-set! str i ch)))))
+    (let lp ((i 0))
+      (cond ((or (= i n) (eof-object? (peek-char in))) i)
+            (else (string-set! str i (read-char in)) (lp (+ i 1))))))))
 
 (define (read-string! str n . o)
-  (if (>= n (string-length str))
+  (if (> n (string-length str))
       (error "string to small to read chars" str n))
   (let* ((in (if (pair? o) (car o) (current-input-port)))
          (res (%read-string! str n in)))
diff --git a/tests/io-tests.scm b/tests/io-tests.scm
index 134fac16..d434d31a 100644
--- a/tests/io-tests.scm
+++ b/tests/io-tests.scm
@@ -23,6 +23,32 @@
   (call-with-input-string "abc\ndef"
     (lambda (in) (let ((line (read-line in))) (list line (read-line in))))))
 
+(test "read-string" '("abc" "def")
+  (call-with-input-string "abcdef"
+    (lambda (in) (let ((str (read-string 3 in))) (list str (read-string 3 in))))))
+
+(test "read-string-to-eof" '("abc" "de")
+  (call-with-input-string "abcde"
+    (lambda (in) (let ((str (read-string 3 in))) (list str (read-string 3 in))))))
+
+(test "read-string!" '("abc" "def")
+  (call-with-input-string "abcdef"
+    (lambda (in)
+      (let* ((str1 (make-string 3))
+             (str2 (make-string 3)))
+        (read-string! str1 3 in)
+        (read-string! str2 3 in)
+        (list str1 str2)))))
+
+(test "read-string!-to-eof" '("abc" "de ")
+  (call-with-input-string "abcde"
+    (lambda (in)
+      (let* ((str1 (make-string 3))
+             (str2 (make-string 3 #\space)))
+        (read-string! str1 3 in)
+        (read-string! str2 3 in)
+        (list str1 str2)))))
+
 (test "null-output-port" #t
   (let ((out (make-null-output-port)))
     (write 1 out)