diff --git a/library/aes.c b/library/aes.c
index 9f20744..2da86c7 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1049,6 +1049,14 @@
     int i;
     unsigned char temp[16];
 
+    AES_VALIDATE_RET( ctx != NULL );
+    AES_VALIDATE_RET( mode == MBEDTLS_AES_ENCRYPT ||
+                      mode == MBEDTLS_AES_DECRYPT );
+    AES_VALIDATE_RET( iv != NULL );
+    AES_VALIDATE_RET( input != NULL );
+    AES_VALIDATE_RET( output != NULL );
+
+
     if( length % 16 )
         return( MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH );