diff --git a/src/fpk.c b/src/fpk.c
index 55ad015..683e74d 100644
--- a/src/fpk.c
+++ b/src/fpk.c
@@ -1,9 +1,21 @@
+#if !defined(_WIN32)
+#define _FILE_OFFSET_BITS 64
+#define _POSIX_C_SOURCE 200809L
+#endif
+
 #include "fpk.h"
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
+#if defined(_WIN32)
+#define fpk_fseek64(f, off) _fseeki64((f), (off), SEEK_SET)
+#else
+#include <sys/types.h>
+#define fpk_fseek64(f, off) fseeko((f), (off_t)(off), SEEK_SET)
+#endif
+
 #define FPK_HEADER_FIELD_ENTRY_COUNT 4
 #define FPK_HEADER_FIELD_DIR_OFFSET 12
 #define FPK_HEADER_FIELD_STRTAB_OFFSET 20
@@ -104,7 +116,7 @@ struct fpk *fpk_open(const char *path)
 	fpk->strtab = malloc((size_t)strtab_size);
 	if (fpk->strtab == NULL)
 		goto fail;
-	if (fseek(fpk->file, (long)strtab_offset, SEEK_SET) != 0)
+	if (fpk_fseek64(fpk->file, strtab_offset) != 0)
 		goto fail;
 	if (fread(fpk->strtab, 1, (size_t)strtab_size, fpk->file) !=
 	    strtab_size)
@@ -113,7 +125,7 @@ struct fpk *fpk_open(const char *path)
 	fpk->entries = malloc((size_t)fpk->entry_count * sizeof(fpk_entry_t));
 	if (fpk->entries == NULL)
 		goto fail;
-	if (fseek(fpk->file, (long)dir_offset, SEEK_SET) != 0)
+	if (fpk_fseek64(fpk->file, dir_offset) != 0)
 		goto fail;
 	for (i = 0; i < fpk->entry_count; i++) {
 		unsigned char rec[FPK_DIR_ENTRY_SIZE];
@@ -173,7 +185,7 @@ void *fpk_read(struct fpk *fpk, const fpk_entry_t *entry, size_t *out_size)
 	if (buf == NULL)
 		goto out;
 
-	if (fseek(fpk->file, (long)entry->data_offset, SEEK_SET) != 0 ||
+	if (fpk_fseek64(fpk->file, entry->data_offset) != 0 ||
 	    fread(buf, 1, (size_t)entry->data_size, fpk->file) !=
 		    entry->data_size) {
 		free(buf);
@@ -289,7 +301,7 @@ int fpk_writer_finalize(struct fpk_writer *w)
 	int ret = 0;
 
 	strtab_offset = w->cursor;
-	if (fseek(w->file, (long)strtab_offset, SEEK_SET) != 0) {
+	if (fpk_fseek64(w->file, strtab_offset) != 0) {
 		ret = -1;
 		goto out;
 	}
@@ -330,7 +342,7 @@ int fpk_writer_finalize(struct fpk_writer *w)
 	put_u64le(header + FPK_HEADER_FIELD_DIR_OFFSET, dir_offset);
 	put_u64le(header + FPK_HEADER_FIELD_STRTAB_OFFSET, strtab_offset);
 
-	if (fseek(w->file, 0, SEEK_SET) != 0 ||
+	if (fpk_fseek64(w->file, 0) != 0 ||
 	    fwrite(header, 1, FPK_HEADER_SIZE, w->file) != FPK_HEADER_SIZE ||
 	    fflush(w->file) != 0)
 		ret = -1;