diff --git a/src/cpu.c b/src/cpu.c
index 33c0231..514abbe 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -37,11 +37,11 @@ void cpu_update(struct cpu_sensors_t *c) {
 	clock_gettime(CLOCK_MONOTONIC, &curr.ts);
 	fast_read_num_u64("/sys/class/powercap/intel-rapl:0/", "energy_uj", buf, &curr.energy, 1);
 
-	const uint64_t tdiff_us = timespec_diff_us(&curr.ts, &prev.ts);
-	c->ptotal = (float)(curr.energy - prev.energy) / (float)tdiff_us;
-	prev = curr;
+	c->ptotal = (float)(curr.energy - prev.energy) / (float)timespec_diff_us(&curr.ts, &prev.ts);
 	if (c->ptotal > 500.0f || c->ptotal < 0.0f)
 		c->ptotal = 0.0f;
+	else
+		prev = curr;
 
 	// lots of reads but still faster than reading /proc/cpuinfo
 	c->avg_freq = 0;