diff --git a/library/gcm.c b/library/gcm.c
index 35823e3..7821204 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -147,7 +147,7 @@
         return MBEDTLS_ERR_GCM_BAD_INPUT;
     }
 
-    if (cipher_info->block_size != 16) {
+    if (mbedtls_cipher_info_get_block_size(cipher_info) != 16) {
         return MBEDTLS_ERR_GCM_BAD_INPUT;
     }