diff --git a/Storage/Disk/DiskImage/Formats/AcornADF.cpp b/Storage/Disk/DiskImage/Formats/AcornADF.cpp
index 27eb68b1a..663af4376 100644
--- a/Storage/Disk/DiskImage/Formats/AcornADF.cpp
+++ b/Storage/Disk/DiskImage/Formats/AcornADF.cpp
@@ -10,36 +10,71 @@
 
 #include "Utility/ImplicitSectors.hpp"
 
-namespace {
-	constexpr int sectors_per_track = 16;
-	constexpr int sector_size = 1;
-}
-
 using namespace Storage::Disk;
 
 AcornADF::AcornADF(const std::string &file_name) : MFMSectorDump(file_name) {
 	// Check that the disk image contains a whole number of sector.
 	using sizeT = decltype(file_.stats().st_size);
-	if(file_.stats().st_size % sizeT(128 << sector_size)) throw Error::InvalidFormat;
+	const auto size = file_.stats().st_size;
+
+	if(size < 1024) throw Error::InvalidFormat;
+
+	// Definitely true: a directory signature of 'Hugo' can be read by both 8-bit
+	// machines and the Archimedes. 'Nick' can be read only by the Archimedes.
+	//
+	// https://mdfs.net/Docs/Comp/Disk/Format/ADFS then falsely states that:
+	//
+	//		The type of ADFS filesystem can be determined by looking for the "Hugo"/
+	//		"Nick" identifier that marks the start of the root directory 512 bytes into
+	//		the filesystem and 1024 bytes in.
+	//
+	// In terms of .ADF files:
+	//
+	//	all 8-bit files seem to have 'Hugo' at offset 513;
+	//	ADFS-D (early Arc, late BBC Master) has 'Nick' or 'Hugo' at 1025; but
+	//	ADFS-E (most Arc) has 'Hugo' at 2049.
+	//
+	// Even allowing for the document having failed to account for the directory ID,
+	// I can't reconcile that 2049 offset with being 1024 bytes into the file system.
+	//
+	// That document claims that ADFS-D and ADFS-E are logically interleaved but
+	// https://github.com/android444/fluxengine/blob/master/doc/disk-acornadfs.md
+	// states that:
+	//
+	//		Acorn logical block numbering goes all the way up side 0 and then all the
+	//		way up side 1. However, FluxEngine uses traditional disk images with alternating
+	//		sides, with the blocks from track 0 side 0 then track 0 side 1 then track 1 side 0 etc.
+	//		Most Acorn emulators will use both formats, but they might require nudging as the side
+	//		order can't be reliably autodetected.
+	//
+	// So then .ADF files might be track-interleaved and might not be.
+
+	switch(size) {
+		default:
+			sector_size_ = 1;
+			sectors_per_track_ = 16;
+		break;
+	}
 
 	// Check that the disk image is at least large enough to hold an ADFS catalogue.
-	if(file_.stats().st_size < 7 * sizeT(128 << sector_size)) throw Error::InvalidFormat;
+	if(file_.stats().st_size < 7 * sizeT(128 << sector_size_)) throw Error::InvalidFormat;
 
 	// Check that the initial directory's 'Hugo's or 'Nick's are present.
+	// TODO: check other locations, to pick sector size and count.
 	file_.seek(513, SEEK_SET);
 	uint8_t bytes[4];
 	file_.read(bytes, 4);
-	if(memcmp(bytes, "Hugo", 4)) throw Error::InvalidFormat;
+	if(memcmp(bytes, "Hugo", 4) && memcmp(bytes, "Nick", 4)) throw Error::InvalidFormat;
 
 	file_.seek(0x6fb, SEEK_SET);
 	file_.read(bytes, 4);
-	if(memcmp(bytes, "Hugo", 4)) throw Error::InvalidFormat;
+	if(memcmp(bytes, "Hugo", 4) && memcmp(bytes, "Nick", 4)) throw Error::InvalidFormat;
 
 	// Pick a number of heads; treat this image as double sided if it's too large to be single-sided.
-	head_count_ = 1 + (file_.stats().st_size > sectors_per_track * sizeT(128 << sector_size) * 80);
+	head_count_ = 1 + (file_.stats().st_size > sectors_per_track_ * sizeT(128 << sector_size_) * 80);
 
 	// Announce disk geometry.
-	set_geometry(sectors_per_track, sector_size, 0, Encodings::MFM::Density::Double);
+	set_geometry(sectors_per_track_, sector_size_, 0, Encodings::MFM::Density::Double);
 }
 
 HeadPosition AcornADF::get_maximum_head_position() {
@@ -51,5 +86,5 @@ int AcornADF::get_head_count() {
 }
 
 long AcornADF::get_file_offset_for_position(Track::Address address) {
-	return (address.position.as_int() * head_count_ + address.head) * (128 << sector_size) * sectors_per_track;
+	return (address.position.as_int() * head_count_ + address.head) * (128 << sector_size_) * sectors_per_track_;
 }
diff --git a/Storage/Disk/DiskImage/Formats/AcornADF.hpp b/Storage/Disk/DiskImage/Formats/AcornADF.hpp
index 54a8d12e7..68a446ec7 100644
--- a/Storage/Disk/DiskImage/Formats/AcornADF.hpp
+++ b/Storage/Disk/DiskImage/Formats/AcornADF.hpp
@@ -33,6 +33,8 @@ class AcornADF: public MFMSectorDump {
 	private:
 		long get_file_offset_for_position(Track::Address address) final;
 		int head_count_ = 1;
+		uint8_t sector_size_ = 1;
+		int sectors_per_track_ = 16;
 };
 
 }