diff --git a/library/aes.c b/library/aes.c
index f6dc9963e..1c743f95d 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1298,6 +1298,9 @@ int mbedtls_aes_crypt_cfb128( mbedtls_aes_context *ctx,
 
     n = *iv_off;
 
+    if( n > 16 )
+        return( MBEDTLS_ERR_AES_BAD_INPUT_DATA );
+
     if( mode == MBEDTLS_AES_DECRYPT )
     {
         while( length-- )
@@ -1391,6 +1394,9 @@ int mbedtls_aes_crypt_ofb( mbedtls_aes_context *ctx,
 
     n = *iv_off;
 
+    if( n > 16 )
+        return( MBEDTLS_ERR_AES_BAD_INPUT_DATA );
+
     while( length-- )
     {
         if( n == 0 )