diff --git a/library/cipher.c b/library/cipher.c
index 4a4a3e4..6153b33 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -399,6 +399,11 @@
             return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
         }
     }
+#if defined(MBEDTLS_CHACHAPOLY_C)
+    if ( ctx->cipher_info->type == MBEDTLS_CIPHER_CHACHA20_POLY1305 &&
+         iv_len != 12 )
+        return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+#endif
 #endif
 
     if ( actual_iv_size != 0 )