diff --git a/manual/arith.texi b/manual/arith.texi
index df6d25e0ba..9f442e4bdd 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -96,16 +96,28 @@ one of these:
 @item uint_fast64_t
 @end itemize
 
-If you want an integer with the widest range possible on the platform on
-which it is being used, use one of the following.  If you use these,
-you should write code that takes into account the variable size and range
-of the integer.
+If you want an integer with a wide range, use one of these:
 
 @itemize @bullet
 @item intmax_t
 @item uintmax_t
 @end itemize
 
+@noindent
+The @code{intmax_t} type is wide enough to hold any signed integer value,
+with the possible exceptions of signed bit-precise integer types,
+and of @code{int@var{N}_t} types that are wider than @code{long long int}.
+Compilers may also support other integer types wider than
+@code{intmax_t}, such as GCC's @code{__int128}.
+The @code{uintmax_t} type is like @code{intmax_t},
+except for unsigned integers.
+
+Code that uses @code{intmax_t} or @code{uintmax_t} should take into
+account the variable size, range and alignment of the types.
+For example, it is unwise for a public interface to rely on @code{intmax_t},
+as the interface's ABI can change if a different compiler
+defines @code{intmax_t} differently.
+
 @Theglibc{} also provides macros that tell you the maximum and
 minimum possible values for each integer data type.  The macro names
 follow these examples: @code{INT32_MAX}, @code{UINT8_MAX},