diff --git a/lib/setup.h b/lib/setup.h
index 36e4c7f14..1d78dc6d2 100644
--- a/lib/setup.h
+++ b/lib/setup.h
@@ -244,4 +244,8 @@ typedef struct hostent Curl_addrinfo;
 typedef struct in_addr Curl_ipconnect;
 #endif
 
+#ifndef SIZEOF_CURL_OFF_T
+#define SIZEOF_CURL_OFF_T sizeof(curl_off_t)
+#endif
+
 #endif /* __CONFIG_H */
diff --git a/src/setup.h b/src/setup.h
index 7e8428d70..340a46a4b 100644
--- a/src/setup.h
+++ b/src/setup.h
@@ -112,4 +112,8 @@ int fileno( FILE *stream);
 #define typedef_bool
 #endif
 
+#ifndef SIZEOF_CURL_OFF_T
+#define SIZEOF_CURL_OFF_T sizeof(curl_off_t)
+#endif
+
 #endif /* __SETUP_H */