diff --git a/src/ChangeLog b/src/ChangeLog
index 4994aaa9fa8..1d3d4d65174 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,7 @@
 2011-03-23  Paul Eggert  <eggert@cs.ucla.edu>
 
+	* cm.c (calccost): Turn while-do into do-while, for clarity.
+
 	Fix more problems found by GCC 4.5.2's static checks.
 
 	* coding.c (encode_coding_raw_text): Avoid unnecessary test
diff --git a/src/cm.c b/src/cm.c
index 6379955b48c..42f855f1694 100644
--- a/src/cm.c
+++ b/src/cm.c
@@ -214,8 +214,9 @@ calccost (struct tty_display_info *tty,
     }
     totalcost = c * deltay;
     if (doit)
-	while (--deltay >= 0)
+      do
           emacs_tputs (tty, p, 1, cmputc);
+      while (0 < --deltay);
 x:
     if ((deltax = dstx - srcx) == 0)
 	goto done;
@@ -296,8 +297,9 @@ fail:
     }
     totalcost += c * deltax;
     if (doit)
-	while (--deltax >= 0)
+      do
           emacs_tputs (tty, p, 1, cmputc);
+      while (0 < --deltax);
 done:
     return totalcost;
 }