diff --git a/library/rsa.c b/library/rsa.c
index ae4382b..d438247 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -139,7 +139,7 @@
      * several calculations are done in place and temporarily change
      * the values of D and E.
      *
-     * Specifically, D is replaced the largest odd divisor of DE - 1
+     * Specifically, D is replaced by the largest odd divisor of DE - 1
      * throughout the calculations.
      */