diff --git a/substitution.c b/substitution.c
index 5129476..ebda538 100644
--- a/substitution.c
+++ b/substitution.c
@@ -58,7 +58,7 @@ void substitute(string plaintext, string key)
         {
             if (isupper(plaintext[i]))
             {
-                printf("%c", key[plaintext[i] - 65]);
+                printf("%c", toupper(key[plaintext[i] - 65]));
             }
             else
             {