diff --git a/src/device.c b/src/device.c
index d7c80be7a..fa7378c1a 100644
--- a/src/device.c
+++ b/src/device.c
@@ -637,16 +637,24 @@ device_get_instance(void)
 const char *
 device_get_config_string(const char *str)
 {
-    const device_config_t *cfg = device_current.dev->config;
+    const char *ret = "";
 
-    while (cfg && cfg->type != CONFIG_END) {
-        if (!strcmp(str, cfg->name))
-            return (config_get_string((char *) device_current.name, (char *) str, (char *) cfg->default_string));
+    if (device_current.dev != NULL) {
+        const device_config_t *cfg = device_current.dev->config;
 
-        cfg++;
+        while ((cfg != NULL) && (cfg->type != CONFIG_END)) {
+            if (!strcmp(str, cfg->name)) {
+                const char *s = (config_get_string((char *) device_current.name,
+                                 (char *) str, (char *) cfg->default_string));
+                ret = (s == NULL) ? "" : s;
+                break;
+            }
+
+            cfg++;
+        }
     }
 
-    return (NULL);
+    return ret;
 }
 
 int
@@ -870,24 +878,29 @@ machine_get_config_int(char *str)
     return 0;
 }
 
-char *
+const char *
 machine_get_config_string(char *str)
 {
-    const device_t        *dev = machine_get_device(machine);
-    const device_config_t *cfg;
+    const device_t *dev = machine_get_device(machine);
+    const char     *ret = "";
 
-    if (dev == NULL)
-        return 0;
+    if (dev != NULL) {
+        const device_config_t *cfg;
 
-    cfg = dev->config;
-    while (cfg && cfg->type != CONFIG_END) {
-        if (!strcmp(str, cfg->name))
-            return (config_get_string((char *) dev->name, str, (char *) cfg->default_string));
+        cfg = dev->config;
+        while ((cfg != NULL) && (cfg->type != CONFIG_END)) {
+            if (!strcmp(str, cfg->name)) {
+                const char *s = config_get_string((char *) dev->name, str,
+                                                  (char *) cfg->default_string);
+                ret = (s == NULL) ? "" : s;
+                break;
+            }
 
-        cfg++;
+            cfg++;
+        }
     }
 
-    return NULL;
+    return ret;
 }
 
 const device_t *
diff --git a/src/device/serial_passthrough.c b/src/device/serial_passthrough.c
index 3da2e09ff..256f9eaa9 100644
--- a/src/device/serial_passthrough.c
+++ b/src/device/serial_passthrough.c
@@ -260,7 +260,7 @@ static const device_config_t serial_passthrough_config[] = {
         .name           = "host_serial_path",
         .description    = "Host Serial Device",
         .type           = CONFIG_SERPORT,
-        .default_string = "",
+        .default_string = NULL,
         .default_int    = 0,
         .file_filter    = NULL,
         .spinner        = { 0 },
diff --git a/src/include/86box/device.h b/src/include/86box/device.h
index 6902ffdfd..b5a4c1925 100644
--- a/src/include/86box/device.h
+++ b/src/include/86box/device.h
@@ -231,8 +231,8 @@ extern int         device_get_instance(void);
 
 extern const char *device_get_internal_name(const device_t *dev);
 
-extern int   machine_get_config_int(char *str);
-extern char *machine_get_config_string(char *str);
+extern int         machine_get_config_int(char *str);
+extern const char *machine_get_config_string(char *str);
 
 extern const device_t device_none;
 extern const device_t device_internal;