diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -1167,7 +1167,6 @@
 native_clock_source_init(void)
 {
 	i8254_init();
-	tsc_init();
 }
 
 static void
diff --git a/sys/i386/i386/machdep.c b/sys/i386/i386/machdep.c
--- a/sys/i386/i386/machdep.c
+++ b/sys/i386/i386/machdep.c
@@ -208,7 +208,6 @@
 i386_clock_source_init(void)
 {
 	i8254_init();
-	tsc_init();
 }
 
 static void
diff --git a/sys/x86/isa/clock.c b/sys/x86/isa/clock.c
--- a/sys/x86/isa/clock.c
+++ b/sys/x86/isa/clock.c
@@ -129,6 +129,7 @@
 	mtx_init(&clock_lock, "clk", NULL, MTX_SPIN | MTX_NOPROFILE);
 	/* Init the clock in order to use DELAY */
 	init_ops.early_clock_source_init();
+	tsc_init();
 }
 
 static int
diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c
--- a/sys/x86/x86/tsc.c
+++ b/sys/x86/x86/tsc.c
@@ -147,6 +147,21 @@
 	tsc_early_calib_exact = 1;
 }
 
+static void
+tsc_freq_xen(void)
+{
+	u_int regs[4];
+
+	/*
+	 * Must run *after* generic tsc_freq_cpuid_vm, so that when Xen is
+	 * emulating Viridian support the Viridian leaf is used instead.
+	 */
+	KASSERT(hv_high >= 0x40000003, ("Invalid max hypervisor leaf on Xen"));
+	cpuid_count(0x40000003, 0, regs);
+	tsc_freq = (uint64_t)(regs[2]) * 1000;
+	tsc_early_calib_exact = 1;
+}
+
 /*
  * Calculate TSC frequency using information from the CPUID leaf 0x15 'Time
  * Stamp Counter and Nominal Core Crystal Clock'.  If leaf 0x15 is not
@@ -358,6 +373,12 @@
 			printf(
 		    "Early TSC frequency %juHz derived from VMWare hypercall\n",
 			    (uintmax_t)tsc_freq);
+	} else if (vm_guest == VM_GUEST_XEN) {
+		tsc_freq_xen();
+		if (bootverbose)
+			printf(
+			"Early TSC frequency %juHz derived from Xen CPUID\n",
+			    (uintmax_t)tsc_freq);
 	} else if (tsc_freq_cpuid(&tsc_freq)) {
 		/*
 		 * If possible, use the value obtained from CPUID as the initial