diff --git a/sys/src/cmd/diff/diff.h b/sys/src/cmd/diff/diff.h
index 76fe050df..34a5dc010 100644
--- a/sys/src/cmd/diff/diff.h
+++ b/sys/src/cmd/diff/diff.h
@@ -22,5 +22,6 @@ Biobuf *prepare(int, char *);
 void panic(int, char *, ...);
 void check(Biobuf *, Biobuf *);
 void change(int, int, int, int);
+void fileheader(void);
 void flushchanges(void);
 
diff --git a/sys/src/cmd/diff/diffio.c b/sys/src/cmd/diff/diffio.c
index 4f291ca26..146bef3bc 100644
--- a/sys/src/cmd/diff/diffio.c
+++ b/sys/src/cmd/diff/diffio.c
@@ -267,22 +267,16 @@ change(int a, int b, int c, int d)
 	if (a > b && c > d)
 		return;
 	anychange = 1;
-	if (firstchange == 0) {
-		if (mflag) {
-			if(mode) {
-				buf[0] = '-';
-				buf[1] = mode;
-				buf[2] = ' ';
-				buf[3] = '\0';
-			} else {
-				buf[0] = '\0';
-			}
-			Bprint(&stdout, "diff %s%s %s\n", buf, file1, file2);
-		}
-		if (mode == 'u') {
-			Bprint(&stdout, "--- %s\n", file1);
-			Bprint(&stdout, "+++ %s\n", file2);
+	if (mflag && firstchange == 0) {
+		if(mode) {
+			buf[0] = '-';
+			buf[1] = mode;
+			buf[2] = ' ';
+			buf[3] = '\0';
+		} else {
+			buf[0] = '\0';
 		}
+		Bprint(&stdout, "diff %s%s %s\n", buf, file1, file2);
 		firstchange = 1;
 	}
 	verb = a > b ? 'a': c > d ? 'd': 'c';
@@ -345,6 +339,15 @@ changeset(int i)
 	return nchanges;
 }
 
+void
+fileheader(void)
+{
+	if(mode != 'u')
+		return;
+	Bprint(&stdout, "--- %s\n", file1);
+	Bprint(&stdout, "+++ %s\n", file2);
+}
+
 void
 flushchanges(void)
 {
diff --git a/sys/src/cmd/diff/diffreg.c b/sys/src/cmd/diff/diffreg.c
index 7ef855994..6f6f144fc 100644
--- a/sys/src/cmd/diff/diffreg.c
+++ b/sys/src/cmd/diff/diffreg.c
@@ -285,6 +285,7 @@ output(void)
 	m = len[0];
 	J[0] = 0;
 	J[m+1] = len[1]+1;
+	fileheader();
 	if (mode != 'e') {
 		for (i0 = 1; i0 <= m; i0 = i1+1) {
 			while (i0 <= m && J[i0] == J[i0-1]+1)