diff --git a/Makefile b/Makefile
index 9c18b8a..5b4139f 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@ MAGIC_CFLAGS=-DHAVE_MAGIC
 MAGIC_LIBS=-lmagic
 
 CC=gcc
-CFLAGS+=-Wall -pedantic -std=c99 -D_POSIX_C_SOURCE=20120607L $(MAGIC_CFLAGS)
+CFLAGS+=-Wall -pedantic -std=c99 -D_POSIX_C_SOURCE=20120607L -D_FILE_OFFSET_BITS=64 $(MAGIC_CFLAGS)
 LIBS=-lmicrohttpd $(MAGIC_LIBS)
 
 TARGET=fileshare
diff --git a/dirlisting.c b/dirlisting.c
index dd54924..dd65bb0 100644
--- a/dirlisting.c
+++ b/dirlisting.c
@@ -21,11 +21,11 @@
 
 struct Entry {
   char *name;
-  size_t size;
+  off_t size;
   uint8_t flags;
 };
 
-const char* format_size(size_t s) {
+const char* format_size(off_t s) {
   static char buf[32];
   const char *prefixes = " kMGTPEZY";
   float fs = s;