diff --git a/library/aes.c b/library/aes.c
index da94b19..3bb8515 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1082,6 +1082,9 @@
     int c, i;
     size_t n = *nc_off;
 
+    if ( n > 0x0F )
+        return( MBEDTLS_ERR_AES_BAD_INPUT_DATA );
+
     while( length-- )
     {
         if( n == 0 ) {