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