diff --git a/src/partition/repart.c b/src/partition/repart.c
index af319d2e33c..356fd9152c5 100644
--- a/src/partition/repart.c
+++ b/src/partition/repart.c
@@ -4318,8 +4318,18 @@ static int parse_argv(int argc, char *argv[]) {
         if (arg_image && arg_root)
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Please specify either --root= or --image=, the combination of both is not supported.");
         else if (!arg_image && !arg_root && in_initrd()) {
-                /* Default to operation on /sysroot when invoked in the initrd! */
-                arg_root = strdup("/sysroot");
+
+                /* By default operate on /sysusr/ or /sysroot/ when invoked in the initrd. We prefer the
+                 * former, if it is mounted, so that we have deterministic behaviour on systems where /usr/
+                 * is vendor-supplied but the root fs formatted on first boot. */
+                r = path_is_mount_point("/sysusr/usr", NULL, 0);
+                if (r <= 0) {
+                        if (r < 0 && r != -ENOENT)
+                                log_debug_errno(r, "Unable to determine whether /sysusr/usr is a mount point, assuming it is not: %m");
+
+                        arg_root = strdup("/sysroot");
+                } else
+                        arg_root = strdup("/sysusr");
                 if (!arg_root)
                         return log_oom();
         }
@@ -4471,8 +4481,43 @@ static int acquire_root_devno(
         return 0;
 }
 
+static int find_os_prefix(const char **ret) {
+        int r;
+
+        assert(ret);
+
+        /* Searches for the right place to look for the OS root. This is relevant in the initrd: in the
+         * initrd the host OS is typically mounted to /sysroot/ — except in setups where /usr/ is a separate
+         * partition, in which case it is mounted to /sysusr/usr/ before being moved to /sysroot/usr/. */
+
+        if (!in_initrd()) {
+                *ret = NULL; /* no prefix */
+                return 0;
+        }
+
+        r = path_is_mount_point("/sysroot", NULL, 0);
+        if (r < 0 && r != -ENOENT)
+                log_debug_errno(r, "Failed to determine whether /sysroot/ is a mount point, assuming it is not: %m");
+        else if (r > 0) {
+                log_debug("/sysroot/ is a mount point, assuming it's the prefix.");
+                *ret = "/sysroot";
+                return 0;
+        }
+
+        r = path_is_mount_point("/sysusr/usr", NULL, 0);
+        if (r < 0 && r != -ENOENT)
+                log_debug_errno(r, "Failed to determine whether /sysusr/usr is a mount point, assuming it is not: %m");
+        else if (r > 0) {
+                log_debug("/sysusr/usr/ is a mount point, assuming /sysusr/ is the prefix.");
+                *ret = "/sysusr";
+                return 0;
+        }
+
+        return -ENOENT;
+}
+
 static int find_root(char **ret, int *ret_fd) {
-        const char *t;
+        const char *t, *prefix;
         int r;
 
         assert(ret);
@@ -4513,12 +4558,16 @@ static int find_root(char **ret, int *ret_fd) {
          * latter we check for cases where / is a tmpfs and only /usr is an actual persistent block device
          * (think: volatile setups) */
 
+        r = find_os_prefix(&prefix);
+        if (r < 0)
+                return log_error_errno(r, "Failed to determine OS prefix: %m");
+
         FOREACH_STRING(t, "/", "/usr") {
                 _cleanup_free_ char *j = NULL;
                 const char *p;
 
-                if (in_initrd()) {
-                        j = path_join("/sysroot", t);
+                if (prefix) {
+                        j = path_join(prefix, t);
                         if (!j)
                                 return log_oom();