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-rw-r--r--gnu/build/file-systems.scm7
1 files changed, 6 insertions, 1 deletions
diff --git a/gnu/build/file-systems.scm b/gnu/build/file-systems.scm
index 3b831c0ec0..3e0873377a 100644
--- a/gnu/build/file-systems.scm
+++ b/gnu/build/file-systems.scm
@@ -245,7 +245,12 @@ Trailing spaces are trimmed."
"Find and read the first primary volume descriptor, starting at OFFSET.
Return #f if not found."
(let* ((sblock (read-superblock device offset 2048 iso9660-superblock?))
- (type-code (if sblock (array-ref sblock 0) 255)))
+ (type-code (if sblock
+ (bytevector-u8-ref sblock 0)
+ (error (format #f
+ "Could not read ISO9660 primary
+volume descriptor from ~s"
+ device)))))
(match type-code
(255 #f) ; Volume Descriptor Set Terminator.
(1 sblock) ; Primary Volume Descriptor