diff --git a/Storage/Disk/DiskImage/Formats/AcornADF.cpp b/Storage/Disk/DiskImage/Formats/AcornADF.cpp
index 5db4e51ba..3b4a1c7c4 100644
--- a/Storage/Disk/DiskImage/Formats/AcornADF.cpp
+++ b/Storage/Disk/DiskImage/Formats/AcornADF.cpp
@@ -9,6 +9,7 @@
 #include "AcornADF.hpp"
 
 #include <sys/stat.h>
+#include "../../Encodings/MFM/Constants.hpp"
 #include "../../Encodings/MFM/Encoder.hpp"
 #include "../../Track/TrackSerialiser.hpp"
 #include "../../Encodings/MFM/SegmentParser.hpp"
@@ -90,7 +91,7 @@ std::shared_ptr<Track> AcornADF::get_track_at_position(unsigned int head, unsign
 void AcornADF::set_track_at_position(unsigned int head, unsigned int position, const std::shared_ptr<Track> &track) {
 	std::map<size_t, Storage::Encodings::MFM::Sector> sectors =
 		Storage::Encodings::MFM::sectors_from_segment(
-			Storage::Disk::track_serialisation(*track, Time(1, 100000)),
+			Storage::Disk::track_serialisation(*track, Storage::Encodings::MFM::MFMBitLength),
 			true);
 
 	std::vector<uint8_t> parsed_track(sectors_per_track*bytes_per_sector, 0);
diff --git a/Storage/Disk/Encodings/MFM/Constants.hpp b/Storage/Disk/Encodings/MFM/Constants.hpp
index 06fe8a4f1..2fa43e7af 100644
--- a/Storage/Disk/Encodings/MFM/Constants.hpp
+++ b/Storage/Disk/Encodings/MFM/Constants.hpp
@@ -9,6 +9,8 @@
 #ifndef Constants_h
 #define Constants_h
 
+#include "../../../Storage.hpp"
+
 namespace Storage {
 namespace Encodings {
 namespace MFM {
@@ -30,6 +32,9 @@ const uint16_t MFMPostSyncCRCValue		= 0xcdb4;	// the value the CRC generator sho
 const uint8_t MFMIndexSyncByteValue		= 0xc2;
 const uint8_t MFMSyncByteValue			= 0xa1;
 
+const Time MFMBitLength					= Time(1, 100000);
+const Time FMBitLength					= Time(1, 50000);
+
 }
 }
 }