diff --git a/library/cipher.c b/library/cipher.c
index 39c105c..4c7ca3f 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 defined(MBEDTLS_GCM_C)