diff --git a/lib/config-tpf.h b/lib/config-tpf.h
index d1714fdfc..d1eb3d906 100644
--- a/lib/config-tpf.h
+++ b/lib/config-tpf.h
@@ -618,6 +618,9 @@
 /* The size of `short', as computed by sizeof. */
 #define SIZEOF_SHORT 2
 
+/* Define to the size of `long', as computed by sizeof. */
+#define SIZEOF_LONG 8
+
 /* The size of `size_t', as computed by sizeof. */
 #define SIZEOF_SIZE_T 8