diff -upr tcsh-6.18.00_orig/sh.hist.c tcsh-6.18.00_work/sh.hist.c
--- tcsh-6.18.00_orig/sh.hist.c	2013-03-28 10:13:52.165407699 +0100
+++ tcsh-6.18.00_work/sh.hist.c	2013-03-28 10:19:49.168703936 +0100
@@ -99,7 +99,7 @@ hremove(struct Hist *hp)
 
 /* Prune length of history list to specified size by history variable. */
 PG_STATIC void
-discardExcess(int histlen)
+discardExcess(int histlen, int flg)
 {
     struct Hist *hp, *np;
     if (histTail == NULL) {
@@ -110,13 +110,13 @@ discardExcess(int histlen)
      * the list is still too long scan the whole list as before.  But only do a
      * full scan if the list is more than 6% (1/16th) too long. */
     while (histCount > (unsigned)histlen && (np = Histlist.Hnext)) {
-        if (eventno - np->Href >= histlen || histlen == 0)
+        if ((eventno - np->Href >= histlen || histlen == 0) && ! (flg & HIST_MERGE))
             hremove(np), hfree(np);
         else
             break;
     }
     while (histCount > (unsigned)histlen && (np = histTail) != &Histlist) {
-        if (eventno - np->Href >= histlen || histlen == 0)
+        if ((eventno - np->Href >= histlen || histlen == 0) || flg & HIST_MERGE)
             hremove(np), hfree(np);
         else
             break;
@@ -153,7 +153,7 @@ savehist(
     }
     if (sp)
         (void) enthist(++eventno, sp, 1, flg, histlen);
-    discardExcess(histlen);
+    discardExcess(histlen, flg);
 }
 
 #define USE_JENKINS_HASH 1