diff --git a/src/drivers/Qt/avi/fileio.cpp b/src/drivers/Qt/avi/fileio.cpp
index 3068780a..89e5a778 100644
--- a/src/drivers/Qt/avi/fileio.cpp
+++ b/src/drivers/Qt/avi/fileio.cpp
@@ -31,13 +31,31 @@
  */
 
 /*
- * Usefull IO functions.
+ * Useful IO functions.
  */
 
 #include <stdio.h>
 
 #include "gwavi.h"
 
+long long gwavi_t::ftell(FILE *fp)
+{
+#ifdef WIN32
+	return ::_ftelli64(fp);
+#else
+	return ::ftell(fp);
+#endif
+}
+
+int gwavi_t::fseek(FILE *fp, long long offset, int whence)
+{
+#ifdef WIN32
+	return ::_fseeki64( fp, offset, whence );
+#else
+	return ::fseek( fp, offset, whence );
+#endif
+}
+
 int
 gwavi_t::write_int(FILE *out, unsigned int n)
 {
diff --git a/src/drivers/Qt/avi/gwavi.h b/src/drivers/Qt/avi/gwavi.h
index adbb8646..3686349a 100644
--- a/src/drivers/Qt/avi/gwavi.h
+++ b/src/drivers/Qt/avi/gwavi.h
@@ -191,13 +191,15 @@ class gwavi_t
 	struct gwavi_stream_format_v_t stream_format_v;
 	struct gwavi_stream_header_t stream_header_a;
 	struct gwavi_stream_format_a_t stream_format_a;
-	long marker;
+	long long marker;
 	std::vector <gwavi_index_rec_t> offsets;
-	long movi_fpos;
+	long long movi_fpos;
 	int bits_per_pixel;
 	char fourcc[8];
 
 	// helper functions
+	long long ftell(FILE *fp);
+	int fseek(FILE *stream, long long offset, int whence);
 	int write_avi_header(FILE *fp, struct gwavi_header_t *avi_header);
 	int write_stream_header(FILE *fp,
 			struct gwavi_stream_header_t *stream_header);