diff --git a/notes.c b/notes.c
index 8f47c202c5..71cc664b50 100644
--- a/notes.c
+++ b/notes.c
@@ -64,7 +64,7 @@ struct non_note {
 #define CLR_PTR_TYPE(ptr)       ((void *) ((uintptr_t) (ptr) & ~3))
 #define SET_PTR_TYPE(ptr, type) ((void *) ((uintptr_t) (ptr) | (type)))
 
-#define GET_NIBBLE(n, sha1) (((sha1[(n) >> 1]) >> ((~(n) & 0x01) << 2)) & 0x0f)
+#define GET_NIBBLE(n, sha1) ((((sha1)[(n) >> 1]) >> ((~(n) & 0x01) << 2)) & 0x0f)
 
 #define KEY_INDEX (GIT_SHA1_RAWSZ - 1)
 #define FANOUT_PATH_SEPARATORS ((GIT_SHA1_HEXSZ / 2) - 1)