diff --git a/tren.py b/tren.py
index 845c1b4..ed22a1c 100755
--- a/tren.py
+++ b/tren.py
@@ -8,7 +8,7 @@
 PROGNAME = "tren.py"
 BASENAME = PROGNAME.split(".py")[0]
 PROGENV  = BASENAME.upper()
-RCSID = "$Id: tren.py,v 1.213 2010/03/29 20:37:26 tundra Exp $"
+RCSID = "$Id: tren.py,v 1.214 2010/03/30 21:02:35 tundra Exp $"
 VERSION = RCSID.split()[2]
 
 # Copyright Information
@@ -1479,13 +1479,8 @@
         rolling over the count.  If 'fmt' is null on entry, the final
         result length is unlimited.
     """
-    
-    
-    fmtlen   = len(fmt)
+       
     base     = len(alphabet)
-    newval   = ""
-    carry    = None
-
 
     # Do position-wise "addition" via symbol substitution moving from
     # right-to-left adjusting for the fact that not all symbols in the
@@ -1513,9 +1508,16 @@
     # may be a different length than the increment string and that not
     # all characters in the format pattern are guaranteed to exist in
     # the alphabet.
-    
+
+    newval   = ""
+    carry    = None
+    fmtlen   = len(fmt)
+    incrlen  = len(incr)
+    calcsize = max(fmtlen, incrlen)
+
     i = -1
-    while abs(i) <= len(incr):
+    done = False
+    while abs(i) <= calcsize and not done:
 
         sum = 0
 
@@ -1525,7 +1527,8 @@
         if fmt and (abs(i) <= fmtlen) and fmt[i] in alphabet:
             sum +=  alphabet.index(fmt[i])
 
-        sum += alphabet.index(incr[i])
+        if abs(i) <= incrlen:
+            sum += alphabet.index(incr[i])
 
         # Do arithmetic modulo alphabet length
             
@@ -1534,26 +1537,21 @@
         if not carry:
             carry = None
 
+            # We're completely done if we're out of digits in incr and
+            # there's no carry to propagate.  This prevents us from
+            # tacking on leading 0th characters which could overwrite
+            # out-of-alphabet characters in the format field.
+
+            if abs(i-1) > incrlen:
+                done =True
+
         newval = alphabet[digit] + newval
 
         i -= 1
 
     if carry:
         newval = alphabet[carry] + newval
-    
 
-    # Suppress leading alphabet[0] symbols so we don't potentially
-    # overwrite non-alphabet symbols in the format string.  If the
-    # user wants these leading alphabet[0] symbols, they can specify
-    # them in their format string.
-
-    # Never clear out a lone Oth character though
-
-    if newval != alphabet[0]:
-        while newval and newval[0] == alphabet[0]:
-            newval = newval[1:]
-
- 
     # Constrain the results to the length of the original format
     # string, rolling over and warning the user as necessary.  The one
     # exception to this is when a null format string is passed.  This