diff --git a/mm/mm.c b/mm/mm.c
index ad6bed3..745a238 100644
--- a/mm/mm.c
+++ b/mm/mm.c
@@ -27,6 +27,7 @@ static char *program_name = "<no argv[0]>";
 static char *stdin_name = "<stdin>";
 static char *stdout_name = "<stdout>";
 static char *stderr_name = "<stderr>";
+static char *amode = "ab";
 static char *rmode = "rb";
 static char *wmode = "rb+";
 static char *wharsh = "wb";
@@ -273,6 +274,9 @@ int main(int argc, char *argv[]){
 
 	while((c = getopt(argc, argv, "ehi:o:u")) != -1)
 		switch(c){
+		case 'a':
+			io[1].fmode = amode;
+			break;
 		case 'e':
 			Io_fappend(&io[1], stderr, stderr_name);
 			break;