diff --git a/otherbackends/raw.c b/otherbackends/raw.c
index 57130dc6..569d2c62 100644
--- a/otherbackends/raw.c
+++ b/otherbackends/raw.c
@@ -156,6 +156,7 @@ static char *raw_init(const BackendVtable *vt, Seat *seat,
     char *loghost;
 
     raw = snew(Raw);
+    memset(raw, 0, sizeof(Raw));
     raw->plug.vt = &Raw_plugvt;
     raw->backend.vt = vt;
     raw->s = NULL;
diff --git a/otherbackends/rlogin.c b/otherbackends/rlogin.c
index 4e3abffe..b9b21786 100644
--- a/otherbackends/rlogin.c
+++ b/otherbackends/rlogin.c
@@ -233,6 +233,7 @@ static char *rlogin_init(const BackendVtable *vt, Seat *seat,
     char *loghost;
 
     rlogin = snew(Rlogin);
+    memset(rlogin, 0, sizeof(Rlogin));
     rlogin->plug.vt = &Rlogin_plugvt;
     rlogin->backend.vt = vt;
     rlogin->s = NULL;
diff --git a/otherbackends/supdup.c b/otherbackends/supdup.c
index 278e689e..3bde828e 100644
--- a/otherbackends/supdup.c
+++ b/otherbackends/supdup.c
@@ -683,6 +683,7 @@ static char *supdup_init(const BackendVtable *x, Seat *seat,
     const char *utf8 = "\033%G";
 
     supdup = snew(struct supdup_tag);
+    memset(supdup, 0, sizeof(Supdup));
     supdup->plug.vt = &fn_table;
     supdup->backend.vt = &supdup_backend;
     supdup->logctx = logctx;
diff --git a/otherbackends/telnet.c b/otherbackends/telnet.c
index 0011cf0d..819cbcb0 100644
--- a/otherbackends/telnet.c
+++ b/otherbackends/telnet.c
@@ -721,6 +721,7 @@ static char *telnet_init(const BackendVtable *vt, Seat *seat,
     int addressfamily;
 
     telnet = snew(Telnet);
+    memset(telnet, 0, sizeof(Telnet));
     telnet->plug.vt = &Telnet_plugvt;
     telnet->backend.vt = vt;
     telnet->conf = conf_copy(conf);
diff --git a/unix/pty.c b/unix/pty.c
index 46382c06..e379e6cf 100644
--- a/unix/pty.c
+++ b/unix/pty.c
@@ -414,6 +414,7 @@ static void pty_open_master(Pty *pty)
 static Pty *new_pty_struct(void)
 {
     Pty *pty = snew(Pty);
+    memset(pty, 0, sizeof(Pty));
     pty->conf = NULL;
     pty->pending_eof = false;
     bufchain_init(&pty->output_data);
diff --git a/unix/serial.c b/unix/serial.c
index 6c8f9b9e..1e20dd20 100644
--- a/unix/serial.c
+++ b/unix/serial.c
@@ -294,6 +294,7 @@ static char *serial_init(const BackendVtable *vt, Seat *seat,
     seat_set_trust_status(seat, false);
 
     serial = snew(Serial);
+    memset(serial, 0, sizeof(Serial));
     serial->backend.vt = vt;
     *backend_handle = &serial->backend;
 
diff --git a/windows/conpty.c b/windows/conpty.c
index 83cb9635..fd5ef246 100644
--- a/windows/conpty.c
+++ b/windows/conpty.c
@@ -232,6 +232,7 @@ static char *conpty_init(const BackendVtable *vt, Seat *seat,
     seat_set_trust_status(seat, false);
 
     conpty = snew(ConPTY);
+    memset(conpty, 0, sizeof(ConPTY));
     conpty->pseudoconsole = pcon;
     pcon_needs_cleanup = false;
     conpty->outpipe = in_w;
diff --git a/windows/serial.c b/windows/serial.c
index 82146a40..14a89822 100644
--- a/windows/serial.c
+++ b/windows/serial.c
@@ -212,6 +212,7 @@ static char *serial_init(const BackendVtable *vt, Seat *seat,
     seat_set_trust_status(seat, false);
 
     serial = snew(Serial);
+    memset(serial, 0, sizeof(Serial));
     serial->port = INVALID_HANDLE_VALUE;
     serial->out = serial->in = NULL;
     serial->bufsize = 0;