Index: sys/conf/kern.opts.mk
===================================================================
--- sys/conf/kern.opts.mk
+++ sys/conf/kern.opts.mk
@@ -74,6 +74,10 @@
 BROKEN_OPTIONS+= ZFS
 .endif
 
+.if ${MACHINE_CPUARCH} == "riscv"
+BROKEN_OPTIONS+= FORMAT_EXTENSIONS
+.endif
+
 # Things that don't work because the kernel doesn't have the support
 # for them.
 .if ${MACHINE} != "i386" && ${MACHINE} != "amd64"