diff --git a/THANKS b/THANKS
index 9e18e5986..3ee51e703 100644
--- a/THANKS
+++ b/THANKS
@@ -130,6 +130,7 @@ For fixes or providing information which led to a fix:
         Michael Tuexen
          Thomas Wawrzinek
         Mark H. Weaver
+          Göran Weinholt
             Jon Wilson
            Andy Wingo
           Keith Wright
diff --git a/libguile/r6rs-ports.c b/libguile/r6rs-ports.c
index 6ad320af4..9576db8be 100644
--- a/libguile/r6rs-ports.c
+++ b/libguile/r6rs-ports.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 2009 Free Software Foundation, Inc.
+/* Copyright (C) 2009, 2010 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -447,7 +447,7 @@ SCM_DEFINE (scm_lookahead_u8, "lookahead-u8", 1, 0, 0,
 
   result = scm_peek_char (port);
   if (SCM_CHARP (result))
-    result = SCM_I_MAKINUM ((signed char) SCM_CHAR (result));
+    result = SCM_I_MAKINUM ((unsigned char) SCM_CHAR (result));
   else
     result = SCM_EOF_VAL;
 
diff --git a/test-suite/tests/r6rs-ports.test b/test-suite/tests/r6rs-ports.test
index 0b627da1a..7d80ed73d 100644
--- a/test-suite/tests/r6rs-ports.test
+++ b/test-suite/tests/r6rs-ports.test
@@ -52,6 +52,11 @@
            (= (char->integer #\A) (get-u8 port))
            (eof-object? (get-u8 port)))))
 
+  (pass-if "lookahead-u8: result is unsigned"
+    ;; Bug #31081.
+    (let ((port (open-bytevector-input-port #vu8(255))))
+      (= (lookahead-u8 port) 255)))
+
   (pass-if "get-bytevector-n [short]"
     (let* ((port (open-input-string "GNU Guile"))
            (bv (get-bytevector-n port 4)))