diff --git a/lib/config-amigaos.h b/lib/config-amigaos.h
index a9fd56774..99b96d656 100644
--- a/lib/config-amigaos.h
+++ b/lib/config-amigaos.h
@@ -86,6 +86,7 @@
 
 #define SIZEOF_INT 4
 #define SIZEOF_SHORT 2
+#define SIZEOF_SIZE_T 4
 
 #define USE_OPENSSL 1
 #define USE_SSLEAY 1
diff --git a/lib/config-mac.h b/lib/config-mac.h
index 740f1d97c..1f7950ab1 100644
--- a/lib/config-mac.h
+++ b/lib/config-mac.h
@@ -61,6 +61,7 @@
 
 #define SIZEOF_INT              4
 #define SIZEOF_SHORT            2
+#define SIZEOF_SIZE_T           4
 
 #define HAVE_GETNAMEINFO 1
 #define GETNAMEINFO_QUAL_ARG1 const
diff --git a/lib/config-os400.h b/lib/config-os400.h
index dad4d0c35..370fc1138 100644
--- a/lib/config-os400.h
+++ b/lib/config-os400.h
@@ -364,6 +364,9 @@
 /* The size of `short', as computed by sizeof. */
 #define SIZEOF_SHORT            2
 
+/* The size of `size_t', as computed by sizeof. */
+#define SIZEOF_SIZE_T           8
+
 /* Whether long long constants must be suffixed by LL. */
 
 #define HAVE_LL
diff --git a/lib/config-riscos.h b/lib/config-riscos.h
index 98bb7880f..84683aa26 100644
--- a/lib/config-riscos.h
+++ b/lib/config-riscos.h
@@ -350,6 +350,9 @@
 /* The size of `short', as computed by sizeof. */
 #define SIZEOF_SHORT 2
 
+/* The size of `size_t', as computed by sizeof. */
+#define SIZEOF_SIZE_T 4
+
 /* Define if you have the ANSI C header files. */
 #undef STDC_HEADERS
 
diff --git a/lib/config-win32.h b/lib/config-win32.h
index 5ee76065d..67bfec3c0 100644
--- a/lib/config-win32.h
+++ b/lib/config-win32.h
@@ -345,6 +345,13 @@
 /* The size of `short', as computed by sizeof. */
 #define SIZEOF_SHORT 2
 
+/* The size of `size_t', as computed by sizeof. */
+#if defined(_WIN64)
+#  define SIZEOF_SIZE_T 8
+#else
+#  define SIZEOF_SIZE_T 4
+#endif
+
 /* ---------------------------------------------------------------- */
 /*                          STRUCT RELATED                          */
 /* ---------------------------------------------------------------- */
diff --git a/lib/config-win32ce.h b/lib/config-win32ce.h
index 1f417825e..3a5913e99 100644
--- a/lib/config-win32ce.h
+++ b/lib/config-win32ce.h
@@ -322,6 +322,13 @@
 /* The size of `short', as computed by sizeof. */
 #define SIZEOF_SHORT 2
 
+/* The size of `size_t', as computed by sizeof. */
+#if defined(_WIN64)
+#  define SIZEOF_SIZE_T 8
+#else
+#  define SIZEOF_SIZE_T 4
+#endif
+
 /* ---------------------------------------------------------------- */
 /*                          STRUCT RELATED                          */
 /* ---------------------------------------------------------------- */