diff --git a/top/top.c b/top/top.c
index 2af2a849..0629b1b3 100644
--- a/top/top.c
+++ b/top/top.c
@@ -1963,7 +1963,7 @@ static void calibrate_fields (void) {
             s = scat(s, fmtmk("%*.*s", len, len, h));
          }
 #ifndef USE_X_COLHDR
-         if (EU_XON == w->procflgs[i - 1]) --i;
+         if (i >= 1 && EU_XON == w->procflgs[i - 1]) --i;
 #endif
 
          /* establish the final maxpflgs and prepare to grow the variable column
@@ -1977,6 +1977,7 @@ static void calibrate_fields (void) {
             fit within screen width, including a leading window number */
          *(s = w->columnhdr) = '\0';
          if (Rc.mode_altscr) s = scat(s, " ");
+         w->endpflg = 0;
          for (i = w->totpflgs - 1; -1 < i; i--) {
             f = w->pflgsall[i];
 #ifndef USE_X_COLHDR