diff --git a/lib/exec_shell.c b/lib/exec_shell.c
index 49b7df5bf..18798ebe4 100644
--- a/lib/exec_shell.c
+++ b/lib/exec_shell.c
@@ -33,13 +33,14 @@
 void __attribute__((__noreturn__)) exec_shell(void)
 {
 	const char *shell = getenv("SHELL");
-	char *shellc = xstrdup(shell);
+	char *shellc;
 	const char *shell_basename;
 	char *arg0;
 
 	if (!shell)
 		shell = DEFAULT_SHELL;
 
+	shellc = xstrdup(shell);
 	shell_basename = basename(shellc);
 	arg0 = xmalloc(strlen(shell_basename) + 2);
 	arg0[0] = '-';