diff --git a/src/monocoque/devices/sounddevice.c b/src/monocoque/devices/sounddevice.c
index 9210178..5deec6e 100644
--- a/src/monocoque/devices/sounddevice.c
+++ b/src/monocoque/devices/sounddevice.c
@@ -211,8 +211,16 @@ int sounddev_init(SoundDevice* sounddevice, const char* devname, SoundDeviceSett
     }
 
 
-    usb_generic_shaker_init(sounddevice, mainloop, context, devname, sds.volume, sds.pan, sds.channels, streamname);
-    //usb_generic_shaker_init(sounddevice);
+    // Returned, not discarded: this function is declared int and used to fall
+    // off its end, so new_sound_device() read whatever happened to be in the
+    // return register and treated most devices as failures -- "Could not
+    // initialize Sound Device" for 22 of 24 configured shakers, while their
+    // PulseAudio streams had in fact connected. The devices were freed and
+    // never fed telemetry, so the graph looked correct in qpwgraph and nothing
+    // shook. Being undefined behaviour it varied by build, which is why the
+    // same config worked against a locally compiled monocoque and not the
+    // packaged one.
+    return usb_generic_shaker_init(sounddevice, mainloop, context, devname, sds.volume, sds.pan, sds.channels, streamname);
 }
 
 static const vtable engine_sound_simdevice_vtable = { &sounddev_engine_update, &sounddev_free };
diff --git a/src/monocoque/mgui/uiconfighelper.c b/src/monocoque/mgui/uiconfighelper.c
index b9481b8..4b484ab 100644
--- a/src/monocoque/mgui/uiconfighelper.c
+++ b/src/monocoque/mgui/uiconfighelper.c
@@ -21,6 +21,11 @@ typedef struct pa_devicelist {
 	char description[256];
 } pa_devicelist_t;
 
+static int matches_any(const char *value)
+{
+    return strcmp(value, "default") == 0 || strcmp(value, "all") == 0;
+}
+
 int find_default_config(config_setting_t *configs)
 {
     int count = config_setting_length(configs);
@@ -29,20 +34,20 @@ int find_default_config(config_setting_t *configs)
     {
         config_setting_t *entry = config_setting_get_elem(configs, i);
 
-        const char *sim;
-        const char *api;
-        const char *car;
+        // A key that isn't in the entry doesn't constrain the match. This used
+        // to require all three, which no real config has: conf/monocoque.config
+        // -- the example the README points at -- sets sim and car and never
+        // mentions api, so every entry was skipped, -1 came back, and the
+        // caller dereferenced the NULL that produced.
+        const char *sim = "default";
+        const char *api = "default";
+        const char *car = "default";
 
-        if (!config_setting_lookup_string(entry, "sim", &sim))
-            continue;
-        if (!config_setting_lookup_string(entry, "api", &api))
-            continue;
-        if (!config_setting_lookup_string(entry, "car", &car))
-            continue;
+        config_setting_lookup_string(entry, "sim", &sim);
+        config_setting_lookup_string(entry, "api", &api);
+        config_setting_lookup_string(entry, "car", &car);
 
-        if ((strcmp(sim, "default") == 0 || strcmp(sim, "all") == 0) &&
-            (strcmp(api, "default") == 0 || strcmp(api, "all") == 0) &&
-            (strcmp(car, "default") == 0 || strcmp(car, "all") == 0))
+        if (matches_any(sim) && matches_any(api) && matches_any(car))
         {
             return i;
         }
@@ -137,11 +142,31 @@ void populate_device_list(ListBox *listbox, config_t* cfg)
     config = config_lookup(cfg, "configs");
 
     int config_num = find_default_config(config);
+    if (config_num < 0)
+    {
+        // No entry claims to be the default one: list the first, which is what
+        // a single-entry config means anyway, rather than nothing.
+        config_num = 0;
+    }
 
     config_setting_t* selectedconfig = config_setting_get_elem(config, config_num);
+    if (selectedconfig == NULL)
+    {
+        fprintf(stderr, "No config entry to list devices for\n");
+        return;
+    }
+
     config_setting_t* config_devices = NULL;
     config_devices = config_setting_lookup(selectedconfig, "devices");
-
+    if (config_devices == NULL)
+    {
+        // config_setting_lookup dereferences its argument, so reaching here
+        // with a NULL selectedconfig used to segfault inside libconfig --
+        // gmonocoque died on launch, before drawing a window, for anyone whose
+        // config didn't produce a match above.
+        fprintf(stderr, "Config entry has no devices section\n");
+        return;
+    }
 
     count = config_setting_length(config_devices);
 
diff --git a/src/monocoque/monocoque-cli.c b/src/monocoque/monocoque-cli.c
index aadb1f4..797e9bf 100644
--- a/src/monocoque/monocoque-cli.c
+++ b/src/monocoque/monocoque-cli.c
@@ -88,8 +88,16 @@ int main(int argc, char** argv)
         return 0;
     }
     Parameters* p = NULL;
-    p = malloc(sizeof(Parameters));
-    MonocoqueSettings* ms = malloc(sizeof(MonocoqueSettings));;
+    // calloc, not malloc: a --help or --version run jumps straight to
+    // cleanup_final before a single field is set, and the cleanup path frees
+    // every pointer in both structs. Uninitialised heap made that a free() of
+    // whatever junk was there -- confirmed on Debian forky, where the
+    // released .deb aborted with `free(): invalid pointer` in
+    // monocoquesettingsfree() on `monocoque --help`. Older glibc happened not
+    // to notice, which is the only reason this looked fine on stable and
+    // Fedora.
+    p = calloc(1, sizeof(Parameters));
+    MonocoqueSettings* ms = calloc(1, sizeof(MonocoqueSettings));
 
     ConfigError ppe = getParameters(argc, argv, p);
     if (ppe == E_SUCCESS_AND_EXIT || ppe == E_SOMETHING_BAD)
diff --git a/src/monocoque/monocoque-gui.c b/src/monocoque/monocoque-gui.c
index a2d5769..29949a8 100644
--- a/src/monocoque/monocoque-gui.c
+++ b/src/monocoque/monocoque-gui.c
@@ -91,7 +91,10 @@ int monocoque_initialize(int argc, char** argv)
     }
 
     p = NULL;
-    p = malloc(sizeof(Parameters));
+    // calloc, not malloc: freeparams() walks every pointer in this struct
+    // on the early-exit paths, before getParameters has set them. See the
+    // same change in monocoque-cli.c.
+    p = calloc(1, sizeof(Parameters));
     p->config_dirpath = NULL;
     p->config_filepath = NULL;
     p->log_filename_str = NULL;
diff --git a/src/monocoque/monocoque.c b/src/monocoque/monocoque.c
index b75447c..e27bfef 100644
--- a/src/monocoque/monocoque.c
+++ b/src/monocoque/monocoque.c
@@ -84,8 +84,16 @@ int main(int argc, char** argv)
         return 0;
     }
     Parameters* p = NULL;
-    p = malloc(sizeof(Parameters));
-    MonocoqueSettings* ms = malloc(sizeof(MonocoqueSettings));;
+    // calloc, not malloc: a --help or --version run jumps straight to
+    // cleanup_final before a single field is set, and the cleanup path frees
+    // every pointer in both structs. Uninitialised heap made that a free() of
+    // whatever junk was there -- confirmed on Debian forky, where the
+    // released .deb aborted with `free(): invalid pointer` in
+    // monocoquesettingsfree() on `monocoque --help`. Older glibc happened not
+    // to notice, which is the only reason this looked fine on stable and
+    // Fedora.
+    p = calloc(1, sizeof(Parameters));
+    MonocoqueSettings* ms = calloc(1, sizeof(MonocoqueSettings));
 
     ConfigError ppe = getParameters(argc, argv, p);
     if (ppe == E_SUCCESS_AND_EXIT || ppe == E_SOMETHING_BAD)