diff --git a/LOG b/LOG
index eb1ce9c1a7..2ab1836551 100644
--- a/LOG
+++ b/LOG
@@ -326,3 +326,4 @@
   bfp to instead key off of both the bfp and efp.
     pdhtml.ss
 - added Windows installer using the WiX Toolset
+- fix typo in ordinal format for 12
diff --git a/mats/format.ms b/mats/format.ms
index b83679fea2..aa92244528 100644
--- a/mats/format.ms
+++ b/mats/format.ms
@@ -667,7 +667,7 @@
   (equal? (format "~:r ~:r ~:r ~:r ~:r ~:r ~:r ~:r ~:r ~:r" 0 1 2 3 4 5 6 7 8 9)
           "zeroth first second third fourth fifth sixth seventh eighth ninth")
   (equal? (format "~:r ~:r ~:r ~:r ~:r ~:r ~:r ~:r ~:r ~:r" 10 11 12 13 14 15 16 17 18 19)
-          "tenth eleventh twelveth thirteenth fourteenth fifteenth sixteenth seventeenth eighteenth nineteenth")
+          "tenth eleventh twelfth thirteenth fourteenth fifteenth sixteenth seventeenth eighteenth nineteenth")
 )
 
 (mat format-fixed1
diff --git a/s/format.ss b/s/format.ss
index ca3fcc4e9e..6cbc13fd6d 100644
--- a/s/format.ss
+++ b/s/format.ss
@@ -1011,7 +1011,7 @@
         (define v20 '#(#f #f twenty thirty forty fifty sixty seventy eighty ninety))
         (define v0 '#(zero one two three four five six seven eight nine ten eleven twelve thirteen fourteen fifteen sixteen seventeen eighteen nineteen))
         (define *v20 '#(#f #f twentieth thirtieth fortieth fiftieth sixtieth seventieth eightieth ninetieth))
-        (define *v0 '#(zeroth first second third fourth fifth sixth seventh eighth ninth tenth eleventh twelveth thirteenth fourteenth fifteenth sixteenth seventeenth eighteenth nineteenth))
+        (define *v0 '#(zeroth first second third fourth fifth sixth seventh eighth ninth tenth eleventh twelfth thirteenth fourteenth fifteenth sixteenth seventeenth eighteenth nineteenth))
         (define (write-ordinal x op)
           (if (<= -999999999 x +999999999)
               (if (< x 0)