--- a/doc/functions/fseek.texi
+++ b/doc/functions/fseek.texi
@@ -18,6 +18,7 @@
 On Windows platforms (excluding Cygwin), this function does not set @code{errno}
 upon failure.
 @item
-On platforms where @code{off_t} is a 32-bit type, @code{fseek} does not work
-correctly with files larger than 2 GB.  The fix is to use fseeko instead.
+On platforms where @code{long} is a 32-bit type, @code{fseek} does not work
+correctly with files larger than 2 GB.  The fix is to use @code{fseeko}
+instead and to invoke the @code{AC_SYS_LARGEFILE} macro.
 @end itemize

--- a/doc/functions/ftell.texi
+++ b/doc/functions/ftell.texi
@@ -19,6 +19,7 @@
 on input streams that are opened in @code{O_TEXT} mode and whose contents
 contains Unix line terminators (LF), on some platforms: mingw.
 @item
-On platforms where @code{off_t} is a 32-bit type, @code{ftell} does not work
-correctly with files larger than 2 GB.  The fix is to use ftello instead.
+On platforms where @code{long} is a 32-bit type, @code{ftell} does not work
+correctly with files larger than 2 GB.  The fix is to use @code{ftello}
+instead and to invoke the @code{AC_SYS_LARGEFILE} macro.
 @end itemize