diff --git a/ChangeLog b/ChangeLog
index 80da006..2329e6c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2005-05-02  Richard B. Kreckel  <kreckel@ginac.de>
+
+	* doc/cln.tex: Document what to do on a x86_64 machine with 32-bit
+	userland.
+
 2005-05-01  Richard B. Kreckel  <kreckel@ginac.de>
 
 	Fix crashes in find_univpoly_ring and related functions
diff --git a/doc/cln.tex b/doc/cln.tex
index 146f81b..019eeee 100644
--- a/doc/cln.tex
+++ b/doc/cln.tex
@@ -438,6 +438,18 @@ on all architectures.  Try disabling them if you run into linker
 problems.  Also, they are generally somewhat slower than static
 libraries so runtime-critical applications should be linked statically.
 
+If you are compiling on a 64-bit machine with 32-bit userland, you
+might have to specify that explicitly while configuring the library.
+For instance, the popular x86_64 architecture can host a 32-bit x86
+operating system and toolchain on top of a 64-bit kernel.  In such a
+situation, you must explicitly tell configure @emph{not} to assume a
+64-bit OS:
+@example
+$ ./configure --build=i686-pc-linux-gnu
+@end example
+If you forget about this, the build will fail because @code{uname -m}
+will set x86_64 which conflicts with what the compiler knows.
+
 If you use @code{g++} from gcc-3.1 with option @samp{-g}, you will need
 some disk space: 335 MB for building as both a shared and a static library,
 or 130 MB when building as a shared library only.