diff --git a/docs/primitives/symmetric-encryption.rst b/docs/primitives/symmetric-encryption.rst
index 6aa7ed2..7081e01 100644
--- a/docs/primitives/symmetric-encryption.rst
+++ b/docs/primitives/symmetric-encryption.rst
@@ -21,7 +21,7 @@
     [...]
 
 Here ``key`` is the encryption key (which must be kept secret), and ``iv`` is
-the initialization vector (which should be random). Exactly what form these
+the initialization vector (which must be random). Exactly what form these
 values should take is described for each of the ciphers and modes.
 
 ``encrypt()`` should be called repeatedly with additional plaintext, and it