diff --git a/Source/Core/DiscIO/Blob.cpp b/Source/Core/DiscIO/Blob.cpp
index 9ed8577c38..1a2333f198 100644
--- a/Source/Core/DiscIO/Blob.cpp
+++ b/Source/Core/DiscIO/Blob.cpp
@@ -77,23 +77,19 @@ bool SectorReader::Read(u64 offset, u64 size, u8* out_ptr)
 			continue;
 		}
 
+		const u8* data = GetBlockData(block);
+		if (!data)
+			return false;
+
 		u32 toCopy = m_blocksize - positionInBlock;
 		if (toCopy >= remain)
 		{
-			const u8* data = GetBlockData(block);
-			if (!data)
-				return false;
-
 			// Yay, we are done!
 			memcpy(out_ptr, data + positionInBlock, (size_t)remain);
 			return true;
 		}
 		else
 		{
-			const u8* data = GetBlockData(block);
-			if (!data)
-				return false;
-
 			memcpy(out_ptr, data + positionInBlock, toCopy);
 			out_ptr += toCopy;
 			remain -= toCopy;
diff --git a/Source/Core/DiscIO/CISOBlob.cpp b/Source/Core/DiscIO/CISOBlob.cpp
index fa9b30e2f5..f9947d0e6c 100644
--- a/Source/Core/DiscIO/CISOBlob.cpp
+++ b/Source/Core/DiscIO/CISOBlob.cpp
@@ -44,7 +44,7 @@ CISOFileReader* CISOFileReader::Create(const std::string& filename)
 
 u64 CISOFileReader::GetDataSize() const
 {
-	return GetRawSize();
+	return CISO_MAP_SIZE * m_block_size;
 }
 
 u64 CISOFileReader::GetRawSize() const
diff --git a/Source/Core/DiscIO/CISOBlob.h b/Source/Core/DiscIO/CISOBlob.h
index a1b5ae5cb7..dd0095f5a4 100644
--- a/Source/Core/DiscIO/CISOBlob.h
+++ b/Source/Core/DiscIO/CISOBlob.h
@@ -37,7 +37,11 @@ public:
 	static CISOFileReader* Create(const std::string& filename);
 
 	BlobType GetBlobType() const override { return BlobType::CISO; }
+
+	// The CISO format does not save the original file size.
+	// This function returns an upper bound.
 	u64 GetDataSize() const override;
+
 	u64 GetRawSize() const override;
 	bool Read(u64 offset, u64 nbytes, u8* out_ptr) override;
 
diff --git a/Source/Core/DiscIO/WbfsBlob.cpp b/Source/Core/DiscIO/WbfsBlob.cpp
index 9607f15f3c..7aaa09c8b1 100644
--- a/Source/Core/DiscIO/WbfsBlob.cpp
+++ b/Source/Core/DiscIO/WbfsBlob.cpp
@@ -39,6 +39,8 @@ WbfsFileReader::WbfsFileReader(const std::string& filename)
 	m_wlba_table = new u16[m_blocks_per_disc];
 	m_files[0]->file.Seek(m_hd_sector_size + WII_DISC_HEADER_SIZE /*+ i * m_disc_info_size*/, SEEK_SET);
 	m_files[0]->file.ReadBytes(m_wlba_table, m_blocks_per_disc * sizeof(u16));
+	for (size_t i = 0; i < m_blocks_per_disc; i++)
+		m_wlba_table[i] = Common::swap16(m_wlba_table[i]);
 }
 
 WbfsFileReader::~WbfsFileReader()
@@ -49,6 +51,11 @@ WbfsFileReader::~WbfsFileReader()
 	delete[] m_wlba_table;
 }
 
+u64 WbfsFileReader::GetDataSize() const
+{
+	return WII_SECTOR_COUNT * WII_SECTOR_SIZE;
+}
+
 bool WbfsFileReader::OpenFiles(const std::string& filename)
 {
 	m_total_files = 0;
@@ -81,37 +88,26 @@ bool WbfsFileReader::OpenFiles(const std::string& filename)
 
 bool WbfsFileReader::ReadHeader()
 {
-	m_files[0]->file.Seek(4, SEEK_SET);
-
 	// Read hd size info
-	m_files[0]->file.ReadBytes(&m_hd_sector_count, 4);
-	m_hd_sector_count = Common::swap32(m_hd_sector_count);
+	m_files[0]->file.ReadBytes(&m_header, sizeof(WbfsHeader));
+	m_header.hd_sector_count = Common::swap32(m_header.hd_sector_count);
 
-	m_files[0]->file.ReadBytes(&m_hd_sector_shift, 1);
-	m_hd_sector_size = 1ull << m_hd_sector_shift;
+	m_hd_sector_size = 1ull << m_header.hd_sector_shift;
 
-	if (m_size != (m_hd_sector_count * m_hd_sector_size))
+	if (m_size != (m_header.hd_sector_count * m_hd_sector_size))
 		return false;
 
 	// Read wbfs cluster info
-	m_files[0]->file.ReadBytes(&m_wbfs_sector_shift, 1);
-	m_wbfs_sector_size = 1ull << m_wbfs_sector_shift;
+	m_wbfs_sector_size = 1ull << m_header.wbfs_sector_shift;
 	m_wbfs_sector_count = m_size / m_wbfs_sector_size;
 
 	if (m_wbfs_sector_size < WII_SECTOR_SIZE)
 		return false;
 
-	m_blocks_per_disc = (WII_SECTOR_COUNT * WII_SECTOR_SIZE) / m_wbfs_sector_size;
-	m_disc_info_size = align(WII_DISC_HEADER_SIZE + m_blocks_per_disc * 2, m_hd_sector_size);
+	m_blocks_per_disc = (WII_SECTOR_COUNT * WII_SECTOR_SIZE + m_wbfs_sector_size - 1) / m_wbfs_sector_size;
+	m_disc_info_size = align(WII_DISC_HEADER_SIZE + m_blocks_per_disc * sizeof(u16), m_hd_sector_size);
 
-	// Read disc table
-	m_files[0]->file.Seek(2, SEEK_CUR);
-	m_files[0]->file.ReadBytes(m_disc_table, 500);
-
-	if (m_disc_table[0] == 0)
-		return false;
-
-	return true;
+	return m_header.disc_table[0] != 0;
 }
 
 bool WbfsFileReader::Read(u64 offset, u64 nbytes, u8* out_ptr)
@@ -122,7 +118,7 @@ bool WbfsFileReader::Read(u64 offset, u64 nbytes, u8* out_ptr)
 		File::IOFile& data_file = SeekToCluster(offset, &read_size);
 		if (read_size == 0)
 			return false;
-		read_size = (read_size > nbytes) ? nbytes : read_size;
+		read_size = std::min(read_size, nbytes);
 
 		if (!data_file.ReadBytes(out_ptr, read_size))
 		{
@@ -140,10 +136,10 @@ bool WbfsFileReader::Read(u64 offset, u64 nbytes, u8* out_ptr)
 
 File::IOFile& WbfsFileReader::SeekToCluster(u64 offset, u64* available)
 {
-	u64 base_cluster = (offset >> m_wbfs_sector_shift);
+	u64 base_cluster = (offset >> m_header.wbfs_sector_shift);
 	if (base_cluster < m_blocks_per_disc)
 	{
-		u64 cluster_address = m_wbfs_sector_size * Common::swap16(m_wlba_table[base_cluster]);
+		u64 cluster_address = m_wbfs_sector_size * m_wlba_table[base_cluster];
 		u64 cluster_offset = offset & (m_wbfs_sector_size - 1);
 		u64 final_address = cluster_address + cluster_offset;
 
diff --git a/Source/Core/DiscIO/WbfsBlob.h b/Source/Core/DiscIO/WbfsBlob.h
index 746798edc6..ce9d42953e 100644
--- a/Source/Core/DiscIO/WbfsBlob.h
+++ b/Source/Core/DiscIO/WbfsBlob.h
@@ -20,7 +20,12 @@ public:
 	static WbfsFileReader* Create(const std::string& filename);
 
 	BlobType GetBlobType() const override { return BlobType::WBFS; }
-	u64 GetDataSize() const override { return m_size; }
+
+	// The WBFS format does not save the original file size.
+	// This function returns a constant upper bound
+	// (the size of a double-layer Wii disc).
+	u64 GetDataSize() const override;
+
 	u64 GetRawSize() const override { return m_size; }
 	bool Read(u64 offset, u64 nbytes, u8* out_ptr) override;
 
@@ -48,15 +53,21 @@ private:
 	u64 m_size;
 
 	u64 m_hd_sector_size;
-	u8 m_hd_sector_shift;
-	u32 m_hd_sector_count;
-
 	u64 m_wbfs_sector_size;
-	u8 m_wbfs_sector_shift;
 	u64 m_wbfs_sector_count;
 	u64 m_disc_info_size;
 
-	u8 m_disc_table[500];
+#pragma pack(1)
+	struct WbfsHeader
+	{
+		char magic[4];
+		u32 hd_sector_count;
+		u8 hd_sector_shift;
+		u8 wbfs_sector_shift;
+		u8 padding[2];
+		u8 disc_table[500];
+	} m_header;
+#pragma pack()
 
 	u16* m_wlba_table;
 	u64 m_blocks_per_disc;
diff --git a/Source/Core/DolphinWX/ISOProperties.cpp b/Source/Core/DolphinWX/ISOProperties.cpp
index c790098ca9..0344e98130 100644
--- a/Source/Core/DolphinWX/ISOProperties.cpp
+++ b/Source/Core/DolphinWX/ISOProperties.cpp
@@ -57,6 +57,7 @@
 #include "Core/GeckoCodeConfig.h"
 #include "Core/PatchEngine.h"
 #include "Core/Boot/Boot.h"
+#include "DiscIO/Blob.h"
 #include "DiscIO/Filesystem.h"
 #include "DiscIO/Volume.h"
 #include "DiscIO/VolumeCreator.h"
@@ -1237,8 +1238,8 @@ void CISOProperties::OnComputeMD5Sum(wxCommandEvent& WXUNUSED (event))
 	u64 read_offset = 0;
 	mbedtls_md5_context ctx;
 
-	File::IOFile file(OpenGameListItem.GetFileName(), "rb");
-	u64 game_size = file.GetSize();
+	std::unique_ptr<DiscIO::IBlobReader> file(DiscIO::CreateBlobReader(OpenGameListItem.GetFileName()));
+	u64 game_size = file->GetDataSize();
 
 	wxProgressDialog progressDialog(
 		_("Computing MD5 checksum"),
@@ -1254,13 +1255,14 @@ void CISOProperties::OnComputeMD5Sum(wxCommandEvent& WXUNUSED (event))
 
 	while(read_offset < game_size)
 	{
-		if (!progressDialog.Update((int)((double)read_offset / (double)game_size * 1000), _("Computing MD5 checksum")))
+		if (!progressDialog.Update((int)((double)read_offset / (double)game_size * 1000)))
 			return;
 
-		size_t read_size;
-		file.ReadArray(&data[0], data.size(), &read_size);
-		mbedtls_md5_update(&ctx, &data[0], read_size);
+		size_t read_size = std::min((u64)data.size(), game_size - read_offset);
+		if (!file->Read(read_offset, read_size, data.data()))
+			return;
 
+		mbedtls_md5_update(&ctx, data.data(), read_size);
 		read_offset += read_size;
 	}