--- top.c
+++ top.c
@@ -930,6 +930,14 @@
    rewind(fp);
    fflush(fp);
 
+ /* save the previous values of cpus[Cpu_tot](i.e. u_sav, s_sav, n_sav, i_sav,
+    * w_sav, x_sav, y_sav) to cpus[cpu_max] before any changes to cpus[], so these
+    * values are not overwritten when copying cpus[cpu_max] back to cpus[Cpu_tot]
+    * at the end of this function.
+    */
+   if (cpu_max != Cpu_tot)
+      memcpy(&cpus[cpu_max], &cpus[Cpu_tot], sizeof(CPU_t));
+
    // first value the last slot with the cpu summary line
    if (!fgets(buf, sizeof(buf), fp)) std_err("failed /proc/stat read");
    cpus[cpu_max].x = 0;  // FIXME: can't tell by kernel version number