diff --git a/src/lsp/ffi.lsp b/src/lsp/ffi.lsp
index 1453266af..bb4fd1f09 100644
--- a/src/lsp/ffi.lsp
+++ b/src/lsp/ffi.lsp
@@ -71,14 +71,15 @@ does not include any Lisp storage overhead."
           ((atom type)
            (error "~A is not a valid foreign type identifier" name))
           ((eq (setf name (first type)) :struct)
-           (setf size (slot-position type nil)
-                 align (apply #'max (mapcar #'(lambda (field)
-                                                (multiple-value-bind (field-size field-align)
-                                                    (size-of-foreign-type (second field))
-                                                  (declare (ignore field-size))
-                                                  field-align))
-                                            (rest type))))
-           (%align-data size align))
+           (setf size (slot-position type nil))
+           (when (rest type)
+             (setf align (apply #'max (mapcar #'(lambda (field)
+                                                  (multiple-value-bind (field-size field-align)
+                                                      (size-of-foreign-type (second field))
+                                                    (declare (ignore field-size))
+                                                    field-align))
+                                              (rest type))))
+             (%align-data size align)))
           ((eq name :array)
            (unless (and (setf size (third type)) (realp size))
              (error "Incomplete foreign type: ~S" type))