diff --git a/src/libsystemd/sd-journal/journal-file.c b/src/libsystemd/sd-journal/journal-file.c
index baabb92fd7..11e251748a 100644
--- a/src/libsystemd/sd-journal/journal-file.c
+++ b/src/libsystemd/sd-journal/journal-file.c
@@ -4694,8 +4694,9 @@ bool journal_file_rotate_suggested(JournalFile *f, usec_t max_file_usec, int log
         return false;
 }
 
-bool journal_file_writable(JournalFile *f) {
+bool journal_file_writable(const JournalFile *f) {
         assert(f);
+
         return (f->open_flags & O_ACCMODE_STRICT) != O_RDONLY;
 }
 
diff --git a/src/libsystemd/sd-journal/journal-file.h b/src/libsystemd/sd-journal/journal-file.h
index 4a5e0d81e2..68317f1308 100644
--- a/src/libsystemd/sd-journal/journal-file.h
+++ b/src/libsystemd/sd-journal/journal-file.h
@@ -378,4 +378,4 @@ static inline uint32_t COMPRESSION_TO_HEADER_INCOMPATIBLE_FLAG(Compression c) {
         }
 }
 
-bool journal_file_writable(JournalFile *f);
+bool journal_file_writable(const JournalFile *f) _pure_;