diff --git a/src/shared/varlink-idl-common.c b/src/shared/varlink-idl-common.c
index a20ec4c429..1dc44cd16c 100644
--- a/src/shared/varlink-idl-common.c
+++ b/src/shared/varlink-idl-common.c
@@ -18,7 +18,7 @@ SD_VARLINK_DEFINE_STRUCT_TYPE(
                 SD_VARLINK_FIELD_COMMENT("64bit inode number of pidfd if known"),
                 SD_VARLINK_DEFINE_FIELD(pidfdId, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("Boot ID of the system the inode number belongs to"),
-                SD_VARLINK_DEFINE_FIELD(bootId, SD_VARLINK_INT, SD_VARLINK_NULLABLE));
+                SD_VARLINK_DEFINE_FIELD(bootId, SD_VARLINK_STRING, SD_VARLINK_NULLABLE));
 
 SD_VARLINK_DEFINE_STRUCT_TYPE(
                 RateLimit,