diff --git a/gnu/packages/cross-base.scm b/gnu/packages/cross-base.scm
index bb3d6d916a..c70739b3ab 100644
--- a/gnu/packages/cross-base.scm
+++ b/gnu/packages/cross-base.scm
@@ -141,6 +141,11 @@ base compiler and using LIBC (which may be either a libc package or #f.)"
                                "--disable-decimal-float" ;would need libc
                                "--disable-libcilkrts"
 
+                               ,@(if (string-prefix? "powerpc9-" target)
+                                     ;; On POWER9 we need this because XXX.
+                                     '("--with-long-double-128")
+                                     '())
+
                                ;; When target is any OS other than 'none' these
                                ;; libraries will fail if there is no libc
                                ;; present. See