diff --git a/ChangeLog b/ChangeLog
index f20299f0f7..8dae3ab1f4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2011-04-27  Eric Blake  <eblake@redhat.com>
+
+	getcwd: fix mingw bugs
+	* m4/getcwd.m4 (gl_FUNC_GETCWD_NULL): Detect one mingw bug.
+	* doc/posix-functions/getcwd.texi (getcwd): Document the problems.
+	* lib/getcwd-lgpl.c (rpl_getcwd): Fix return type.
+
 2011-04-27  Bruno Haible  <bruno@clisp.org>
 
 	mkstemps: Ensure declaration on MacOS X 10.5.
diff --git a/doc/posix-functions/getcwd.texi b/doc/posix-functions/getcwd.texi
index a8dba967ec..1f6dd187d2 100644
--- a/doc/posix-functions/getcwd.texi
+++ b/doc/posix-functions/getcwd.texi
@@ -11,7 +11,12 @@ Portability problems fixed by either Gnulib module @code{getcwd} or
 @itemize
 @item
 On glibc platforms, @code{getcwd (NULL, n)} allocates memory for the result.
-On other platforms, this call is not allowed.
+On some other platforms, this call is not allowed.  Conversely, mingw fails
+to honor non-zero @code{n}.
+@item
+On some platforms, the prototype for @code{getcwd} uses @code{int}
+instead of @code{size_t} for the size argument:
+mingw.
 @end itemize
 
 Portability problems fixed by Gnulib module @code{getcwd}:
diff --git a/lib/getcwd-lgpl.c b/lib/getcwd-lgpl.c
index a5596f8869..53c5562357 100644
--- a/lib/getcwd-lgpl.c
+++ b/lib/getcwd-lgpl.c
@@ -53,7 +53,7 @@ rpl_getcwd (char *buf, size_t size)
       if (!buf)
         {
           errno = ENOMEM;
-          return -1;
+          return NULL;
         }
       result = getcwd (buf, size);
       if (!result)
diff --git a/m4/getcwd.m4 b/m4/getcwd.m4
index 55f937222b..eb2c9d9375 100644
--- a/m4/getcwd.m4
+++ b/m4/getcwd.m4
@@ -6,7 +6,7 @@
 # with or without modifications, as long as this notice is preserved.
 
 # Written by Paul Eggert.
-# serial 5
+# serial 6
 
 AC_DEFUN([gl_FUNC_GETCWD_NULL],
   [
@@ -20,7 +20,8 @@ AC_DEFUN([gl_FUNC_GETCWD_NULL],
 #        endif
 ]], [[
 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
-/* mingw cwd does not start with '/', but getcwd does allocate.  */
+/* mingw cwd does not start with '/', but getcwd does allocate.
+   However, mingw fails to honor non-zero size.  */
 #else
            if (chdir ("/") != 0)
              return 1;
@@ -36,6 +37,9 @@ AC_DEFUN([gl_FUNC_GETCWD_NULL],
                return 0;
              }
 #endif
+         /* If size is non-zero, allocation must fail if size is too small */
+         if (getcwd (NULL, 1))
+           return 5;
          ]])],
         [gl_cv_func_getcwd_null=yes],
         [gl_cv_func_getcwd_null=no],
@@ -45,8 +49,6 @@ AC_DEFUN([gl_FUNC_GETCWD_NULL],
          *-gnu*)               gl_cv_func_getcwd_null="guessing yes";;
                                # Guess yes on Cygwin.
          cygwin*)              gl_cv_func_getcwd_null="guessing yes";;
-                               # Guess yes on mingw.
-         mingw*)               gl_cv_func_getcwd_null="guessing yes";;
                                # If we don't know, assume the worst.
          *)                    gl_cv_func_getcwd_null="guessing no";;
        esac