diff --git a/Documentation/MANPAGE.md b/Documentation/MANPAGE.md
index 9446f0b..aa40922 100644
--- a/Documentation/MANPAGE.md
+++ b/Documentation/MANPAGE.md
@@ -106,6 +106,22 @@ Options:
 :	Allow mounting over non-empty directories. FUSE by default disallows
 	this to prevent accidential shadowing of files.
 
+**-noprealloc**
+:	Disable preallocation before writing. By default, gocryptfs
+	preallocates the space the next write will take using fallocate(2)
+	in mode FALLOC_FL_KEEP_SIZE. The preallocation makes sure it cannot
+	run out of space in the middle of the write, which would cause the
+	last 4kB block to be corrupt and unreadable.
+
+	On ext4, preallocation is fast and does not cause a
+	noticeable performance hit. Unfortunately, on Btrfs, preallocation
+	is very slow, especially on rotational HDDs. The "-noprealloc"
+	option gives users the choice to trade robustness against
+	out-of-space errors for a massive speedup.
+	
+	For benchmarks and more details of the issue see
+	https://github.com/rfjakob/gocryptfs/issues/63 .
+
 **-nosyslog**
 :	Diagnostic messages are normally redirected to syslog once gocryptfs
 	daemonizes. This option disables the redirection and messages will
@@ -197,4 +213,4 @@ Mount an ecrypted view of joe's home directory using reverse mode:
 
 SEE ALSO
 ========
-fuse(8)
+fuse(8) fallocate(2)
diff --git a/cli_args.go b/cli_args.go
index 5751f81..7301d9a 100644
--- a/cli_args.go
+++ b/cli_args.go
@@ -16,7 +16,8 @@ import (
 type argContainer struct {
 	debug, init, zerokey, fusedebug, openssl, passwd, fg, version,
 	plaintextnames, quiet, nosyslog, wpanic,
-	longnames, allow_other, ro, reverse, aessiv, nonempty, raw64 bool
+	longnames, allow_other, ro, reverse, aessiv, nonempty, raw64,
+	noprealloc bool
 	masterkey, mountpoint, cipherdir, cpuprofile, extpass,
 	memprofile, ko, passfile, ctlsock string
 	// Configuration file name override
@@ -105,6 +106,7 @@ func parseCliOpts() (args argContainer) {
 	flagSet.BoolVar(&args.aessiv, "aessiv", false, "AES-SIV encryption")
 	flagSet.BoolVar(&args.nonempty, "nonempty", false, "Allow mounting over non-empty directories")
 	flagSet.BoolVar(&args.raw64, "raw64", false, "Use unpadded base64 for file names")
+	flagSet.BoolVar(&args.noprealloc, "noprealloc", false, "Disable preallocation before writing")
 	flagSet.StringVar(&args.masterkey, "masterkey", "", "Mount with explicit master key")
 	flagSet.StringVar(&args.cpuprofile, "cpuprofile", "", "Write cpu profile to specified file")
 	flagSet.StringVar(&args.memprofile, "memprofile", "", "Write memory profile to specified file")
@@ -116,7 +118,7 @@ func parseCliOpts() (args argContainer) {
 	flagSet.IntVar(&args.notifypid, "notifypid", 0, "Send USR1 to the specified process after "+
 		"successful mount - used internally for daemonization")
 	flagSet.IntVar(&args.scryptn, "scryptn", configfile.ScryptDefaultLogN, "scrypt cost parameter logN. "+
-		"Setting this to a lower value speeds up mounting but makes the password susceptible to brute-force attacks")
+		"A lower value speeds up mounting but makes the password susceptible to brute-force attacks")
 	// Ignored otions
 	var dummyBool bool
 	ignoreText := "(ignored for compatibility)"
diff --git a/internal/fusefrontend/args.go b/internal/fusefrontend/args.go
index d8b0304..eb796cd 100644
--- a/internal/fusefrontend/args.go
+++ b/internal/fusefrontend/args.go
@@ -21,4 +21,6 @@ type Args struct {
 	// Raw64 is true when RawURLEncoding (without padding) should be used for
 	// file names
 	Raw64 bool
+	// NoPrealloc disables automatic preallocation before writing
+	NoPrealloc bool
 }
diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index d637528..5fe866b 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -49,10 +49,12 @@ type file struct {
 	// The opCount is used to judge whether "lastWrittenOffset" is still
 	// guaranteed to be correct.
 	lastOpCount uint64
+	// Parent filesystem
+	fs *FS
 }
 
 // NewFile returns a new go-fuse File instance.
-func NewFile(fd *os.File, writeOnly bool, contentEnc *contentenc.ContentEnc) (nodefs.File, fuse.Status) {
+func NewFile(fd *os.File, writeOnly bool, fs *FS) (nodefs.File, fuse.Status) {
 	var st syscall.Stat_t
 	err := syscall.Fstat(int(fd.Fd()), &st)
 	if err != nil {
@@ -65,10 +67,11 @@ func NewFile(fd *os.File, writeOnly bool, contentEnc *contentenc.ContentEnc) (no
 	return &file{
 		fd:             fd,
 		writeOnly:      writeOnly,
-		contentEnc:     contentEnc,
+		contentEnc:     fs.contentEnc,
 		devIno:         di,
 		fileTableEntry: t,
 		loopbackFile:   nodefs.NewLoopbackFile(fd),
+		fs:             fs,
 	}, fuse.OK
 }
 
@@ -107,10 +110,12 @@ func (f *file) createHeader() (fileID []byte, err error) {
 	h := contentenc.RandomHeader()
 	buf := h.Pack()
 	// Prevent partially written (=corrupt) header by preallocating the space beforehand
-	err = syscallcompat.EnospcPrealloc(int(f.fd.Fd()), 0, contentenc.HeaderLen)
-	if err != nil {
-		tlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.devIno.ino, err.Error())
-		return nil, err
+	if !f.fs.args.NoPrealloc {
+		err = syscallcompat.EnospcPrealloc(int(f.fd.Fd()), 0, contentenc.HeaderLen)
+		if err != nil {
+			tlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.devIno.ino, err.Error())
+			return nil, err
+		}
 	}
 	// Actually write header
 	_, err = f.fd.WriteAt(buf, 0)
@@ -285,7 +290,7 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 		writeChain[i] = blockData
 		numOutBytes += len(blockData)
 	}
-	// Concatenenate all elements in the writeChain into one contigous buffer
+	// Concatenenate all elements in the writeChain into one contiguous buffer
 	tmp := make([]byte, numOutBytes)
 	writeBuf := bytes.NewBuffer(tmp[:0])
 	for _, w := range writeChain {
@@ -293,11 +298,14 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 	}
 	// Preallocate so we cannot run out of space in the middle of the write.
 	// This prevents partially written (=corrupt) blocks.
+	var err error
 	cOff := blocks[0].BlockCipherOff()
-	err := syscallcompat.EnospcPrealloc(int(f.fd.Fd()), int64(cOff), int64(writeBuf.Len()))
-	if err != nil {
-		tlog.Warn.Printf("ino%d fh%d: doWrite: prealloc failed: %s", f.devIno.ino, f.intFd(), err.Error())
-		return 0, fuse.ToStatus(err)
+	if !f.fs.args.NoPrealloc {
+		err = syscallcompat.EnospcPrealloc(int(f.fd.Fd()), int64(cOff), int64(writeBuf.Len()))
+		if err != nil {
+			tlog.Warn.Printf("ino%d fh%d: doWrite: prealloc failed: %s", f.devIno.ino, f.intFd(), err.Error())
+			return 0, fuse.ToStatus(err)
+		}
 	}
 	// Write
 	_, err = f.fd.WriteAt(writeBuf.Bytes(), int64(cOff))
diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index e9e6113..f41e9a7 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -106,7 +106,7 @@ func (fs *FS) Open(path string, flags uint32, context *fuse.Context) (fuseFile n
 		return nil, fuse.ToStatus(err)
 	}
 
-	return NewFile(f, writeOnly, fs.contentEnc)
+	return NewFile(f, writeOnly, fs)
 }
 
 // Create implements pathfs.Filesystem.
@@ -160,7 +160,7 @@ func (fs *FS) Create(path string, flags uint32, mode uint32, context *fuse.Conte
 			tlog.Warn.Printf("Create: Chown failed: %v", err)
 		}
 	}
-	return NewFile(fd, writeOnly, fs.contentEnc)
+	return NewFile(fd, writeOnly, fs)
 }
 
 // Chmod implements pathfs.Filesystem.
diff --git a/mount.go b/mount.go
index 3bafd8c..29d34b8 100644
--- a/mount.go
+++ b/mount.go
@@ -145,6 +145,7 @@ func initFuseFrontend(key []byte, args *argContainer, confFile *configfile.ConfF
 		CryptoBackend:  cryptoBackend,
 		ConfigCustom:   args._configCustom,
 		Raw64:          args.raw64,
+		NoPrealloc:     args.noprealloc,
 	}
 	// confFile is nil when "-zerokey" or "-masterkey" was used
 	if confFile != nil {