diff --git a/library/aes.c b/library/aes.c
index cc1e5ce..4d9a56a 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -771,6 +771,9 @@
     const unsigned char *key1, *key2;
     unsigned int key1bits, key2bits;
 
+    AES_VALIDATE_RET( ctx != NULL );
+    AES_VALIDATE_RET( key != NULL );
+
     ret = mbedtls_aes_xts_decode_keys( key, keybits, &key1, &key1bits,
                                        &key2, &key2bits );
     if( ret != 0 )
@@ -793,6 +796,9 @@
     const unsigned char *key1, *key2;
     unsigned int key1bits, key2bits;
 
+    AES_VALIDATE_RET( ctx != NULL );
+    AES_VALIDATE_RET( key != NULL );
+
     ret = mbedtls_aes_xts_decode_keys( key, keybits, &key1, &key1bits,
                                        &key2, &key2bits );
     if( ret != 0 )