-#define F_LENGTH(f) ((OFF_T)(f)->len32 + ((f)->flags & FLAG_LENGTH64 \
- ? (OFF_T)OPT_EXTRA(f, 0)->unum << 32 : 0u))
+#if SIZEOF_INT64 < 8
+#define F_LENGTH(f) ((int64)(f)->len32)
+#else
+#define F_LENGTH(f) ((int64)(f)->len32 + ((f)->flags & FLAG_LENGTH64 \
+ ? (int64)OPT_EXTRA(f, 0)->unum << 32 : 0))
+#endif