diff --git a/log-tree.c b/log-tree.c
index d3ae969f60..2e2be7c40f 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -469,6 +469,12 @@ int log_tree_diff_flush(struct rev_info *opt)
 			int pch = DIFF_FORMAT_DIFFSTAT | DIFF_FORMAT_PATCH;
 			if ((pch & opt->diffopt.output_format) == pch)
 				printf("---");
+			if (opt->diffopt.output_prefix) {
+				struct strbuf *msg = NULL;
+				msg = opt->diffopt.output_prefix(&opt->diffopt,
+					opt->diffopt.output_prefix_data);
+				fwrite(msg->buf, msg->len, 1, stdout);
+			}
 			putchar('\n');
 		}
 	}