diff --git a/libisofs/fs_image.c b/libisofs/fs_image.c
index 99c5f78..7f28458 100644
--- a/libisofs/fs_image.c
+++ b/libisofs/fs_image.c
@@ -4586,7 +4586,7 @@ int iso_analyze_sun(IsoImage *image, IsoDataSource *src, int flag)
         iso_read_msb(usad + 144, 2) != 0x10 ||
         iso_read_msb(usad + 444, 4) != 0 ||
         sai->image_size > 0x3fffffff ||
-        iso_read_msb(usad + 448, 4) < sai->image_size * 4 - 600 ||
+        iso_read_msb(usad + 448, 4) < ((int64_t) sai->image_size * 4) - 600 ||
         iso_read_msb(usad + 448, 4) > sai->image_size * 4)
         return 0;
     checksum[0] = checksum[1] = 0;