diff --git a/cpp/scsidump/scsidump_core.cpp b/cpp/scsidump/scsidump_core.cpp
index f8c6a70677..9f0da0dd8c 100644
--- a/cpp/scsidump/scsidump_core.cpp
+++ b/cpp/scsidump/scsidump_core.cpp
@@ -379,7 +379,7 @@ pair<uint64_t, uint32_t> ScsiDump::ReadCapacity()
 			(static_cast<uint32_t>(buffer[sector_size_offset + 2]) << 8) |
 			static_cast<uint32_t>(buffer[sector_size_offset + 3]);
 
-    return { capacity, sector_size };
+    return { capacity - sector_size, sector_size };
 }
 
 void ScsiDump::Read(uint32_t bstart, uint32_t blength, int length)