diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 51e15af2ef..b79fb54573 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -4927,7 +4927,7 @@ tramp-maybe-open-connection
 	      (setenv "PS1" tramp-initial-end-of-output)
               (unless (stringp tramp-encoding-shell)
                 (tramp-error vec 'file-error "`tramp-encoding-shell' not set"))
-	      (let* ((current-host (system-name))
+	      (let* ((current-host tramp-system-name)
 		     (target-alist (tramp-compute-multi-hops vec))
 		     ;; We will apply `tramp-ssh-controlmaster-options'
 		     ;; only for the first hop.
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 55f652fa9a..2e32481198 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -175,6 +175,12 @@ tramp-encoding-command-interactive
   :version "24.1"
   :type '(choice (const nil) string))

+;; Since Emacs 26.1, `system-name' can return `nil' at build time if
+;; Emacs is compiled with "--no-build-details".  We do expect it to be
+;; a string.  (Bug#44481)
+(defconst tramp-system-name (or (system-name) "")
+  "The system name Tramp is running locally.")
+
 (defvar tramp-methods nil
   "Alist of methods for remote files.
 This is a list of entries of the form (NAME PARAM1 PARAM2 ...).
@@ -416,7 +422,7 @@ tramp-default-user-alist
 		       (choice :tag "  Host regexp" regexp sexp)
 		       (choice :tag "    User name" string (const nil)))))

-(defcustom tramp-default-host (system-name)
+(defcustom tramp-default-host tramp-system-name
   "Default host to use for transferring files.
 Useful for su and sudo methods mostly."
   :type 'string)
@@ -471,8 +477,8 @@ tramp-save-ad-hoc-proxies
 (defcustom tramp-restricted-shell-hosts-alist
   (when (memq system-type '(windows-nt))
     (list (format "\\`\\(%s\\|%s\\)\\'"
-		  (regexp-quote (downcase (system-name)))
-		  (regexp-quote (upcase (system-name))))))
+		  (regexp-quote (downcase tramp-system-name))
+		  (regexp-quote (upcase tramp-system-name)))))
   "List of hosts, which run a restricted shell.
 This is a list of regular expressions, which denote hosts running
 a restricted shell like \"rbash\".  Those hosts can be used as
@@ -485,7 +491,7 @@ tramp-local-host-regexp
   (concat
    "\\`"
    (regexp-opt
-    (list "localhost" "localhost6" (system-name) "127.0.0.1" "::1") t)
+    (list "localhost" "localhost6" tramp-system-name "127.0.0.1" "::1") t)
    "\\'")
   "Host names which are regarded as local host.
 If the local host runs a chrooted environment, set this to nil."