diff --git a/lib/efi_loader/efi_string.c b/lib/efi_loader/efi_string.c
index 413e329..50d1daf 100644
--- a/lib/efi_loader/efi_string.c
+++ b/lib/efi_loader/efi_string.c
@@ -5,6 +5,8 @@
  * Copyright (c) 2020 AKASHI Takahiro, Linaro Limited
  */
 
+#define LOG_CATEGORY LOGC_EFI
+
 #include <charset.h>
 #include <efi_loader.h>
 #include <malloc.h>