diff --git a/configure.in b/configure.in
index 5d889efb..a997de6f 100644
--- a/configure.in
+++ b/configure.in
@@ -172,6 +172,8 @@ fi
 AC_SUBST(EV_LIB_WS32)
 AC_SUBST(EV_LIB_GDI)
 
+AC_SYS_LARGEFILE
+
 LIBEVENT_OPENSSL
 
 dnl Checks for header files.
@@ -542,6 +544,7 @@ AC_CHECK_SIZEOF(int)
 AC_CHECK_SIZEOF(short)
 AC_CHECK_SIZEOF(size_t)
 AC_CHECK_SIZEOF(void *)
+AC_CHECK_SIZEOF(off_t)
 
 AC_CHECK_TYPES([struct in6_addr, struct sockaddr_in6, sa_family_t, struct addrinfo, struct sockaddr_storage], , ,
 [#define _GNU_SOURCE
diff --git a/evconfig-private.h.in b/evconfig-private.h.in
index cffdf531..254ae509 100644
--- a/evconfig-private.h.in
+++ b/evconfig-private.h.in
@@ -24,6 +24,11 @@
 # undef __EXTENSIONS__
 #endif
 
+/* Number of bits in a file offset, on hosts where this is settable. */
+#undef _FILE_OFFSET_BITS
+/* Define for large files, on AIX-style hosts. */
+#undef _LARGE_FILES
+
 /* Define to 1 if on MINIX. */
 #ifndef _MINIX
 #undef _MINIX
diff --git a/include/event2/util.h b/include/event2/util.h
index c71fdcf5..2494b384 100644
--- a/include/event2/util.h
+++ b/include/event2/util.h
@@ -193,8 +193,21 @@ extern "C" {
 #define ev_ssize_t ssize_t
 #endif
 
+/* Note that we define ev_off_t based on the compile-time size of off_t that
+ * we used to build Libevent, and not based on the current size of off_t.
+ * (For example, we don't define ev_off_t to off_t.).  We do this because
+ * some systems let you build your software with different off_t sizes
+ * at runtime, and so putting in any dependency on off_t would risk API
+ * mismatch.
+ */
 #ifdef _WIN32
 #define ev_off_t ev_int64_t
+#elif _EVENT_SIZEOF_OFF_T == 8
+#define ev_off_t ev_int64_t
+#elif _EVENT_SIZEOF_OFF_T == 4
+#define ev_off_t ev_int32_t
+#elif defined(_EVENT_IN_DOXYGEN)
+#define ev_off_t ...
 #else
 #define ev_off_t off_t
 #endif