--- files/gentoo-config
+++ files/gentoo-config
@@ -41,3 +41,12 @@ INCTIFF = 
 LIBTIFF = -ltiff
 INCX11 =
 LIBX11 = -lX11
+
+# Most people have migrated libX11 to /usr/lib, but just in case ...
+check_x11=$(shell \
+	echo 'int main(){}' > test.c ; \
+	if ! $(CC) test.c -lX11 -o /dev/null 2>/dev/null ; then \
+		echo "-L/usr/X11R6/lib" ; \
+	fi ; \
+	rm -f test.c)
+LIBX11 += $(call check_x11)