diff --git a/attr.c b/attr.c
index 243d60ffa9a6a097514ddfeb74c98ae7bb30f35c..09e7e50d3e4e3548187e230ea9bf20398e0959a0 100644
--- a/attr.c
+++ b/attr.c
@@ -387,7 +387,7 @@ static struct attr_stack *read_attr_from_index(const char *path, int macro_ok)
 	char *buf, *sp;
 	int lineno = 0;
 
-	buf = read_blob_data_from_index(use_index ? use_index : &the_index, path);
+	buf = read_blob_data_from_index(use_index ? use_index : &the_index, path, NULL);
 	if (!buf)
 		return NULL;
 
diff --git a/cache.h b/cache.h
index 5d66c74f6aa3ab0c26e62a668d25a94d0d9bfde7..627776b5e6b6fbd74c44935033c36c8811ba3601 100644
--- a/cache.h
+++ b/cache.h
@@ -307,7 +307,7 @@ extern void free_name_hash(struct index_state *istate);
 #define resolve_undo_clear() resolve_undo_clear_index(&the_index)
 #define unmerge_cache_entry_at(at) unmerge_index_entry_at(&the_index, at)
 #define unmerge_cache(pathspec) unmerge_index(&the_index, pathspec)
-#define read_blob_data_from_cache(path) read_blob_data_from_index(&the_index, (path))
+#define read_blob_data_from_cache(path, sz) read_blob_data_from_index(&the_index, (path), (sz))
 #endif
 
 enum object_type {
@@ -453,7 +453,7 @@ extern int add_file_to_index(struct index_state *, const char *path, int flags);
 extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, int refresh);
 extern int ce_same_name(struct cache_entry *a, struct cache_entry *b);
 extern int index_name_is_other(const struct index_state *, const char *, int);
-extern void *read_blob_data_from_index(struct index_state *, const char *);
+extern void *read_blob_data_from_index(struct index_state *, const char *, unsigned long *);
 
 /* do stat comparison even if CE_VALID is true */
 #define CE_MATCH_IGNORE_VALID		01
diff --git a/read-cache.c b/read-cache.c
index 48d87e83ed062f566800256560272bbadc6492d7..8c27ed2c66345c0a1538932f57c554fcfe5339a5 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1896,7 +1896,7 @@ int index_name_is_other(const struct index_state *istate, const char *name,
 	return 1;
 }
 
-void *read_blob_data_from_index(struct index_state *istate, const char *path)
+void *read_blob_data_from_index(struct index_state *istate, const char *path, unsigned long *size)
 {
 	int pos, len;
 	unsigned long sz;
@@ -1925,5 +1925,7 @@ void *read_blob_data_from_index(struct index_state *istate, const char *path)
 		free(data);
 		return NULL;
 	}
+	if (size)
+		*size = sz;
 	return data;
 }