diff --git a/src/devices/nm-device-private.h b/src/devices/nm-device-private.h
index c5b4936b51..c2ba98f387 100644
--- a/src/devices/nm-device-private.h
+++ b/src/devices/nm-device-private.h
@@ -45,7 +45,7 @@ enum NMActStageReturn {
 
 NMSettings *nm_device_get_settings (NMDevice *self);
 
-void nm_device_set_ip_iface (NMDevice *self, const char *iface);
+gboolean nm_device_set_ip_iface (NMDevice *self, const char *iface);
 
 void nm_device_activate_schedule_stage3_ip_config_start (NMDevice *device);
 
diff --git a/src/devices/nm-device.c b/src/devices/nm-device.c
index 64bb62c893..f172ec2c6f 100644
--- a/src/devices/nm-device.c
+++ b/src/devices/nm-device.c
@@ -848,22 +848,32 @@ nm_device_get_ip_ifindex (NMDevice *self)
 	return priv->ip_iface ? priv->ip_ifindex : priv->ifindex;
 }
 
-void
+/**
+ * nm_device_set_ip_iface:
+ * @self: the #NMDevice
+ * @iface: the new IP interface name
+ *
+ * Updates the IP interface name and possibly the ifindex.
+ *
+ * Returns: %TRUE if the anything (name or ifindex) changed, %FALSE if nothing
+ * changed.
+ */
+gboolean
 nm_device_set_ip_iface (NMDevice *self, const char *iface)
 {
 	NMDevicePrivate *priv;
 	int ifindex;
 
-	g_return_if_fail (NM_IS_DEVICE (self));
+	g_return_val_if_fail (NM_IS_DEVICE (self), FALSE);
 
 	priv = NM_DEVICE_GET_PRIVATE (self);
 	if (nm_streq0 (iface, priv->ip_iface)) {
 		if (!iface)
-			return;
+			return FALSE;
 		ifindex = nm_platform_if_nametoindex (NM_PLATFORM_GET, iface);
 		if (   ifindex <= 0
 		    || priv->ip_ifindex == ifindex)
-			return;
+			return FALSE;
 
 		priv->ip_ifindex = ifindex;
 		_LOGD (LOGD_DEVICE, "ip-ifname: update ifindex for ifname '%s': %d", iface, priv->ip_ifindex);
@@ -904,6 +914,7 @@ nm_device_set_ip_iface (NMDevice *self, const char *iface)
 		priv->ip_mtu = nm_platform_link_get_mtu (NM_PLATFORM_GET, priv->ip_ifindex);
 
 	_notify (self, PROP_IP_IFACE);
+	return TRUE;
 }
 
 static gboolean
diff --git a/src/devices/wwan/nm-device-modem.c b/src/devices/wwan/nm-device-modem.c
index fec0d4ce91..7a70a0bf43 100644
--- a/src/devices/wwan/nm-device-modem.c
+++ b/src/devices/wwan/nm-device-modem.c
@@ -260,16 +260,11 @@ static void
 data_port_changed_cb (NMModem *modem, GParamSpec *pspec, gpointer user_data)
 {
 	NMDevice *self = NM_DEVICE (user_data);
-	const char *old = nm_device_get_ip_iface (self);
-	const char *new = nm_modem_get_data_port (modem);
-	gboolean changed = FALSE;
-
-	if (new && g_strcmp0 (new, old))
-		changed = TRUE;
+	gboolean changed;
 
 	/* We set the IP iface in the device as soon as we know it, so that we
 	 * properly ifup it if needed */
-	nm_device_set_ip_iface (self, new);
+	changed = nm_device_set_ip_iface (self, nm_modem_get_data_port (modem));
 
 	/* Disable IPv6 immediately on the interface since NM handles IPv6
 	 * internally, and leaving it enabled could allow the kernel's IPv6