diff --git a/src/lib/probe.c b/src/lib/probe.c
index 6025d97..01ac26a 100644
--- a/src/lib/probe.c
+++ b/src/lib/probe.c
@@ -24,20 +24,9 @@
 #include "blkid_stub.h"
 #include "log.h"
 #include "probe.h"
+#include "system_stub.h"
 #include "util.h"
 
-/**
- * Factory function to convert a dev_t to the full device path
- */
-static char *cbm_devnode_to_devpath(dev_t dev)
-{
-        autofree(char) *c = NULL;
-        if (asprintf(&c, "/dev/block/%u:%u", major(dev), minor(dev)) < 0) {
-                return NULL;
-        }
-        return realpath(c, NULL);
-}
-
 /**
  * Convert a sysfs dev file to the target device path
  */
@@ -65,7 +54,7 @@ static char *cbm_dev_file_to_devpath(const char *devfile)
                 return NULL;
         }
 
-        return cbm_devnode_to_devpath(makedev(dev_major, dev_minor));
+        return cbm_system_devnode_to_devpath(makedev(dev_major, dev_minor));
 }
 
 static char *cbm_get_luks_uuid(const char *part)
@@ -150,13 +139,9 @@ CbmDeviceProbe *cbm_probe_path(const char *path)
                 LOG_ERROR("Path does not exist: %s", path);
                 return NULL;
         }
-        if (major(st.st_dev) == 0) {
-                LOG_ERROR("Invalid block device: %s", path);
-                return NULL;
-        }
         probe.dev = st.st_dev;
 
-        devnode = cbm_devnode_to_devpath(probe.dev);
+        devnode = cbm_system_devnode_to_devpath(probe.dev);
         if (!devnode) {
                 DECLARE_OOM();
                 return NULL;
diff --git a/src/lib/system_stub.c b/src/lib/system_stub.c
index f349d2d..bfbb795 100644
--- a/src/lib/system_stub.c
+++ b/src/lib/system_stub.c
@@ -16,16 +16,37 @@
 #include <sys/mount.h>
 
 #include "files.h"
+#include "log.h"
+
+/**
+ * Factory function to convert a dev_t to the full device path
+ * This is the default internal function
+ */
+static char *cbm_devnode_to_devpath(dev_t dev)
+{
+        if (major(dev) == 0) {
+                LOG_ERROR("Invalid block device: %u:%u", major(dev), minor(dev));
+                return NULL;
+        }
+
+        autofree(char) *c = NULL;
+        if (asprintf(&c, "/dev/block/%u:%u", major(dev), minor(dev)) < 0) {
+                return NULL;
+        }
+        return realpath(c, NULL);
+}
 
 /**
  * Default vtable for system call passthrough
  */
-static CbmSystemOps default_system_ops = {.mount = mount,
-                                          .umount = umount,
-                                          .system = system,
-                                          .is_mounted = cbm_is_mounted,
-                                          .get_mountpoint_for_device =
-                                              cbm_get_mountpoint_for_device };
+static CbmSystemOps default_system_ops = {
+        .mount = mount,
+        .umount = umount,
+        .system = system,
+        .is_mounted = cbm_is_mounted,
+        .get_mountpoint_for_device = cbm_get_mountpoint_for_device,
+        .devnode_to_devpath = cbm_devnode_to_devpath,
+};
 
 /**
  * Pointer to the currently active vtable
@@ -50,6 +71,7 @@ void cbm_system_set_vtable(CbmSystemOps *ops)
         assert(system_ops->is_mounted != NULL);
         assert(system_ops->get_mountpoint_for_device != NULL);
         assert(system_ops->system != NULL);
+        assert(system_ops->devnode_to_devpath != NULL);
 }
 
 int cbm_system_mount(const char *source, const char *target, const char *filesystemtype,
@@ -78,6 +100,11 @@ char *cbm_system_get_mountpoint_for_device(const char *device)
         return system_ops->get_mountpoint_for_device(device);
 }
 
+char *cbm_system_devnode_to_devpath(dev_t d)
+{
+        return system_ops->devnode_to_devpath(d);
+}
+
 /*
  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  *
diff --git a/src/lib/system_stub.h b/src/lib/system_stub.h
index 3550ca8..558abab 100644
--- a/src/lib/system_stub.h
+++ b/src/lib/system_stub.h
@@ -14,6 +14,7 @@
 #define _GNU_SOURCE
 
 #include <stdbool.h>
+#include <sys/types.h>
 
 /**
  * Defines the vtable used for all systen operations within clr-boot-manager.
@@ -32,6 +33,9 @@ typedef struct CbmSystemOps {
 
         /* exec family */
         int (*system)(const char *command);
+
+        /* dev utility */
+        char *(*devnode_to_devpath)(dev_t t);
 } CbmSystemOps;
 
 /**
@@ -74,6 +78,11 @@ int cbm_system_umount(const char *target);
  */
 int cbm_system_system(const char *command);
 
+/**
+ * Resolve the path for a given dev_t
+ */
+char *cbm_system_devnode_to_devpath(dev_t d);
+
 /*
  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  *
diff --git a/tests/system-harness.h b/tests/system-harness.h
index c5e72d7..23bc4d7 100644
--- a/tests/system-harness.h
+++ b/tests/system-harness.h
@@ -41,6 +41,15 @@ static inline char *test_get_mountpoint_for_device(__cbm_unused__ const char *de
         return NULL;
 }
 
+static inline char *test_devnode_to_devpath(__cbm_unused__ dev_t d)
+{
+        char *a = NULL;
+        if (asprintf(&a, "%s/dev/testRoot", TOP_BUILD_DIR "/tests/update_playground") < 0) {
+                abort();
+        }
+        return a;
+}
+
 /**
  * Default vtable for testing. Copy into a local struct and override specific
  * fields.
@@ -49,7 +58,8 @@ CbmSystemOps SystemTestOps = {.mount = test_mount,
                               .umount = test_umount,
                               .system = test_system,
                               .is_mounted = test_is_mounted,
-                              .get_mountpoint_for_device = test_get_mountpoint_for_device };
+                              .get_mountpoint_for_device = test_get_mountpoint_for_device,
+                              .devnode_to_devpath = test_devnode_to_devpath };
 
 /*
  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html