diff --git a/libguile/numbers.h b/libguile/numbers.h
index 83bcc9ea7..c07082eb1 100644
--- a/libguile/numbers.h
+++ b/libguile/numbers.h
@@ -4,7 +4,7 @@
 #define SCM_NUMBERS_H
 
 /* Copyright (C) 1995, 1996, 1998, 2000-2006, 2008-2011, 2013, 2014,
- *   2016, 2017 Free Software Foundation, Inc.
+ *   2016-2018 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -172,14 +172,18 @@ typedef long scm_t_inum;
 typedef struct scm_t_double
 {
   SCM type;
+#if SCM_SIZEOF_UINTPTR_T != 8
   SCM pad;
+#endif
   double real;
 } scm_t_double;
 
 typedef struct scm_t_complex
 {
   SCM type;
+#if SCM_SIZEOF_UINTPTR_T != 8
   SCM pad;
+#endif
   double real;
   double imag;
 } scm_t_complex;
diff --git a/module/system/base/types.scm b/module/system/base/types.scm
index c6aaed242..834fa5f38 100644
--- a/module/system/base/types.scm
+++ b/module/system/base/types.scm
@@ -1,5 +1,5 @@
 ;;; 'SCM' type tag decoding.
-;;; Copyright (C) 2014, 2015, 2017 Free Software Foundation, Inc.
+;;; Copyright (C) 2014, 2015, 2017, 2018 Free Software Foundation, Inc.
 ;;;
 ;;; This library is free software; you can redistribute it and/or modify it
 ;;; under the terms of the GNU Lesser General Public License as published by
@@ -419,7 +419,7 @@ using BACKEND."
           (((_ & #xffff = %tc16-bignum))
            (inferior-object 'bignum address))
           (((_ & #xffff = %tc16-flonum) pad)
-           (let* ((address (+ address (* 2 %word-size)))
+           (let* ((address (+ address (match %word-size (4 8) (8 8))))
                   (port    (memory-port backend address (sizeof double)))
                   (words   (get-bytevector-n port (sizeof double))))
              (bytevector-ieee-double-ref words 0 (native-endianness))))