Index: head/sys/dev/cpuctl/cpuctl.c
===================================================================
--- head/sys/dev/cpuctl/cpuctl.c
+++ head/sys/dev/cpuctl/cpuctl.c
@@ -367,8 +367,10 @@
 	rdmsr_safe(MSR_BIOS_SIGN, &rev0); /* Get current microcode revision. */
 
 	/*
-	 * Perform update.
+	 * Perform update.  Flush caches first to work around seeingly
+	 * undocumented errata applying to some Broadwell CPUs.
 	 */
+	wbinvd();
 	wrmsr_safe(MSR_BIOS_UPDT_TRIG, (uintptr_t)(ptr));
 	wrmsr_safe(MSR_BIOS_SIGN, 0);