diff --git a/builtin/blame.c b/builtin/blame.c
index e39d9865e2d3f8db10ef2f43b9a2d07ad0b61df9..0aac73665b79df94cf6269f3520fa147b33b6b9b 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -2077,6 +2077,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	if (!contents_from || strcmp("-", contents_from)) {
 		struct stat st;
 		const char *read_from;
+		char *buf_ptr;
 		unsigned long buf_len;
 
 		if (contents_from) {
@@ -2094,10 +2095,8 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 		switch (st.st_mode & S_IFMT) {
 		case S_IFREG:
 			if (DIFF_OPT_TST(opt, ALLOW_TEXTCONV) &&
-			    textconv_object(read_from, mode, null_sha1, &buf.buf, &buf_len)) {
-				buf.alloc = buf_len;
-				buf.len = buf_len;
-			}
+			    textconv_object(read_from, mode, null_sha1, &buf_ptr, &buf_len))
+				strbuf_attach(&buf, buf_ptr, buf_len, buf_len + 1);
 			else if (strbuf_read_file(&buf, read_from, st.st_size) != st.st_size)
 				die_errno("cannot open or read '%s'", read_from);
 			break;