diff --git a/minix/kernel/arch/i386/apic.c b/minix/kernel/arch/i386/apic.c
index 39346b679..c4fa74c1e 100644
--- a/minix/kernel/arch/i386/apic.c
+++ b/minix/kernel/arch/i386/apic.c
@@ -442,7 +442,8 @@ static int spurious_irq_handler(irq_hook_t * UNUSED(hook))
 
 static void apic_calibrate_clocks(unsigned cpu)
 {
-	u32_t lvtt, val, lapic_delta;
+	u32_t lvtt, val;
+	u64_t lapic_delta;
 	u64_t tsc_delta;
 	u64_t cpu_freq;
 
@@ -514,7 +515,8 @@ static void apic_calibrate_clocks(unsigned cpu)
 	lapic_delta = lapic_tctr0 - lapic_tctr1;
 	tsc_delta = tsc1 - tsc0;
 
-	lapic_bus_freq[cpuid] = system_hz * lapic_delta / (PROBE_TICKS - 1);
+	lapic_bus_freq[cpuid] = make64(system_hz,0) * lapic_delta /
+		make64(PROBE_TICKS-1,0);
 	BOOT_VERBOSE(printf("APIC bus freq %u MHz\n",
 				lapic_bus_freq[cpuid] / 1000000));
 	cpu_freq = (tsc_delta / (PROBE_TICKS - 1)) * make64(system_hz, 0);