diff --git a/library/cipher.c b/library/cipher.c
index d51ccd7..4a4a3e4 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -386,6 +386,12 @@
 #if defined(MBEDTLS_CHACHA20_C)
     if ( ctx->cipher_info->type == MBEDTLS_CIPHER_CHACHA20 )
     {
+        /* Even though the actual_iv_size is overwritten with a correct value
+         * of 12 from the cipher info, return an error to indicate that
+         * the input iv_len is wrong. */
+        if( iv_len != 12 )
+            return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+
         if ( 0 != mbedtls_chacha20_starts( (mbedtls_chacha20_context*)ctx->cipher_ctx,
                                            iv,
                                            0U ) ) /* Initial counter value */