diff --git a/internal/ignore/cache.go b/internal/ignore/cache.go
index 3667bcf45..115275b19 100644
--- a/internal/ignore/cache.go
+++ b/internal/ignore/cache.go
@@ -15,26 +15,11 @@
 
 package ignore
 
-import (
-	"sync"
-	"time"
-)
-
-var (
-	caches   = make(map[string]*cache)
-	cacheMut sync.Mutex
-)
-
-func init() {
-	// Periodically go through the cache and remove cache entries that have
-	// not been touched in the last two hours.
-	go cleanIgnoreCaches(2 * time.Hour)
-}
+import "time"
 
 type cache struct {
 	patterns []Pattern
 	entries  map[string]cacheEntry
-	mut      sync.Mutex
 }
 
 type cacheEntry struct {
@@ -50,46 +35,27 @@ func newCache(patterns []Pattern) *cache {
 }
 
 func (c *cache) clean(d time.Duration) {
-	c.mut.Lock()
 	for k, v := range c.entries {
 		if time.Since(v.access) > d {
 			delete(c.entries, k)
 		}
 	}
-	c.mut.Unlock()
 }
 
 func (c *cache) get(key string) (result, ok bool) {
-	c.mut.Lock()
 	res, ok := c.entries[key]
 	if ok {
 		res.access = time.Now()
 		c.entries[key] = res
 	}
-	c.mut.Unlock()
 	return res.value, ok
 }
 
 func (c *cache) set(key string, val bool) {
-	c.mut.Lock()
 	c.entries[key] = cacheEntry{val, time.Now()}
-	c.mut.Unlock()
 }
 
 func (c *cache) len() int {
-	c.mut.Lock()
 	l := len(c.entries)
-	c.mut.Unlock()
 	return l
 }
-
-func cleanIgnoreCaches(dur time.Duration) {
-	for {
-		time.Sleep(dur)
-		cacheMut.Lock()
-		for _, v := range caches {
-			v.clean(dur)
-		}
-		cacheMut.Unlock()
-	}
-}
diff --git a/internal/ignore/ignore.go b/internal/ignore/ignore.go
index e74c7ad21..d1b68c73c 100644
--- a/internal/ignore/ignore.go
+++ b/internal/ignore/ignore.go
@@ -17,6 +17,8 @@ package ignore
 
 import (
 	"bufio"
+	"bytes"
+	"crypto/md5"
 	"fmt"
 	"io"
 	"os"
@@ -24,6 +26,7 @@ import (
 	"regexp"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/syncthing/syncthing/internal/fnmatch"
 )
@@ -33,51 +36,76 @@ type Pattern struct {
 	include bool
 }
 
+func (p Pattern) String() string {
+	if p.include {
+		return p.match.String()
+	} else {
+		return "(?exclude)" + p.match.String()
+	}
+}
+
 type Matcher struct {
-	patterns []Pattern
-	matches  *cache
-	mut      sync.Mutex
+	patterns  []Pattern
+	withCache bool
+	matches   *cache
+	curHash   string
+	stop      chan struct{}
+	mut       sync.Mutex
 }
 
-func Load(file string, cache bool) (*Matcher, error) {
-	seen := make(map[string]bool)
-	matcher, err := loadIgnoreFile(file, seen)
-	if !cache || err != nil {
-		return matcher, err
+func New(withCache bool) *Matcher {
+	m := &Matcher{
+		withCache: withCache,
+		stop:      make(chan struct{}),
 	}
-
-	cacheMut.Lock()
-	defer cacheMut.Unlock()
-
-	// Get the current cache object for the given file
-	cached, ok := caches[file]
-	if !ok || !patternsEqual(cached.patterns, matcher.patterns) {
-		// Nothing in cache or a cache mismatch, create a new cache which will
-		// store matches for the given set of patterns.
-		// Initialize oldMatches to indicate that we are interested in
-		// caching.
-		cached = newCache(matcher.patterns)
-		matcher.matches = cached
-		caches[file] = cached
-		return matcher, nil
+	if withCache {
+		go m.clean(2 * time.Hour)
 	}
-
-	// Patterns haven't changed, so we can reuse the old matches, create a new
-	// matches map and update the pointer. (This prevents matches map from
-	// growing indefinately, as we only cache whatever we've matched in the last
-	// iteration, rather than through runtime history)
-	matcher.matches = cached
-	return matcher, nil
+	return m
 }
 
-func Parse(r io.Reader, file string) (*Matcher, error) {
-	seen := map[string]bool{
-		file: true,
+func (m *Matcher) Load(file string) error {
+	// No locking, Parse() does the locking
+
+	fd, err := os.Open(file)
+	if err != nil {
+		// We do a parse with empty patterns to clear out the hash, cache etc.
+		m.Parse(&bytes.Buffer{}, file)
+		return err
 	}
-	return parseIgnoreFile(r, file, seen)
+	defer fd.Close()
+
+	return m.Parse(fd, file)
+}
+
+func (m *Matcher) Parse(r io.Reader, file string) error {
+	m.mut.Lock()
+	defer m.mut.Unlock()
+
+	seen := map[string]bool{file: true}
+	patterns, err := parseIgnoreFile(r, file, seen)
+	// Error is saved and returned at the end. We process the patterns
+	// (possibly blank) anyway.
+
+	newHash := hashPatterns(patterns)
+	if newHash == m.curHash {
+		// We've already loaded exactly these patterns.
+		return err
+	}
+
+	m.curHash = newHash
+	m.patterns = patterns
+	if m.withCache {
+		m.matches = newCache(patterns)
+	}
+
+	return err
 }
 
 func (m *Matcher) Match(file string) (result bool) {
+	m.mut.Lock()
+	defer m.mut.Unlock()
+
 	if len(m.patterns) == 0 {
 		return false
 	}
@@ -108,18 +136,53 @@ func (m *Matcher) Match(file string) (result bool) {
 
 // Patterns return a list of the loaded regexp patterns, as strings
 func (m *Matcher) Patterns() []string {
+	m.mut.Lock()
+	defer m.mut.Unlock()
+
 	patterns := make([]string, len(m.patterns))
 	for i, pat := range m.patterns {
-		if pat.include {
-			patterns[i] = pat.match.String()
-		} else {
-			patterns[i] = "(?exclude)" + pat.match.String()
-		}
+		patterns[i] = pat.String()
 	}
 	return patterns
 }
 
-func loadIgnoreFile(file string, seen map[string]bool) (*Matcher, error) {
+func (m *Matcher) Hash() string {
+	m.mut.Lock()
+	defer m.mut.Unlock()
+	return m.curHash
+}
+
+func (m *Matcher) Stop() {
+	close(m.stop)
+}
+
+func (m *Matcher) clean(d time.Duration) {
+	t := time.NewTimer(d / 2)
+	for {
+		select {
+		case <-m.stop:
+			return
+		case <-t.C:
+			m.mut.Lock()
+			if m.matches != nil {
+				m.matches.clean(d)
+			}
+			t.Reset(d / 2)
+			m.mut.Unlock()
+		}
+	}
+}
+
+func hashPatterns(patterns []Pattern) string {
+	h := md5.New()
+	for _, pat := range patterns {
+		h.Write([]byte(pat.String()))
+		h.Write([]byte("\n"))
+	}
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+func loadIgnoreFile(file string, seen map[string]bool) ([]Pattern, error) {
 	if seen[file] {
 		return nil, fmt.Errorf("Multiple include of ignore file %q", file)
 	}
@@ -134,8 +197,8 @@ func loadIgnoreFile(file string, seen map[string]bool) (*Matcher, error) {
 	return parseIgnoreFile(fd, file, seen)
 }
 
-func parseIgnoreFile(fd io.Reader, currentFile string, seen map[string]bool) (*Matcher, error) {
-	var exps Matcher
+func parseIgnoreFile(fd io.Reader, currentFile string, seen map[string]bool) ([]Pattern, error) {
+	var patterns []Pattern
 
 	addPattern := func(line string) error {
 		include := true
@@ -150,27 +213,27 @@ func parseIgnoreFile(fd io.Reader, currentFile string, seen map[string]bool) (*M
 			if err != nil {
 				return fmt.Errorf("Invalid pattern %q in ignore file", line)
 			}
-			exps.patterns = append(exps.patterns, Pattern{exp, include})
+			patterns = append(patterns, Pattern{exp, include})
 		} else if strings.HasPrefix(line, "**/") {
 			// Add the pattern as is, and without **/ so it matches in current dir
 			exp, err := fnmatch.Convert(line, fnmatch.FNM_PATHNAME)
 			if err != nil {
 				return fmt.Errorf("Invalid pattern %q in ignore file", line)
 			}
-			exps.patterns = append(exps.patterns, Pattern{exp, include})
+			patterns = append(patterns, Pattern{exp, include})
 
 			exp, err = fnmatch.Convert(line[3:], fnmatch.FNM_PATHNAME)
 			if err != nil {
 				return fmt.Errorf("Invalid pattern %q in ignore file", line)
 			}
-			exps.patterns = append(exps.patterns, Pattern{exp, include})
+			patterns = append(patterns, Pattern{exp, include})
 		} else if strings.HasPrefix(line, "#include ") {
 			includeFile := filepath.Join(filepath.Dir(currentFile), line[len("#include "):])
 			includes, err := loadIgnoreFile(includeFile, seen)
 			if err != nil {
 				return err
 			}
-			exps.patterns = append(exps.patterns, includes.patterns...)
+			patterns = append(patterns, includes...)
 		} else {
 			// Path name or pattern, add it so it matches files both in
 			// current directory and subdirs.
@@ -178,13 +241,13 @@ func parseIgnoreFile(fd io.Reader, currentFile string, seen map[string]bool) (*M
 			if err != nil {
 				return fmt.Errorf("Invalid pattern %q in ignore file", line)
 			}
-			exps.patterns = append(exps.patterns, Pattern{exp, include})
+			patterns = append(patterns, Pattern{exp, include})
 
 			exp, err = fnmatch.Convert("**/"+line, fnmatch.FNM_PATHNAME)
 			if err != nil {
 				return fmt.Errorf("Invalid pattern %q in ignore file", line)
 			}
-			exps.patterns = append(exps.patterns, Pattern{exp, include})
+			patterns = append(patterns, Pattern{exp, include})
 		}
 		return nil
 	}
@@ -218,17 +281,5 @@ func parseIgnoreFile(fd io.Reader, currentFile string, seen map[string]bool) (*M
 		}
 	}
 
-	return &exps, nil
-}
-
-func patternsEqual(a, b []Pattern) bool {
-	if len(a) != len(b) {
-		return false
-	}
-	for i := range a {
-		if a[i].include != b[i].include || a[i].match.String() != b[i].match.String() {
-			return false
-		}
-	}
-	return true
+	return patterns, nil
 }
diff --git a/internal/ignore/ignore_test.go b/internal/ignore/ignore_test.go
index 27a4c3c77..20c36e905 100644
--- a/internal/ignore/ignore_test.go
+++ b/internal/ignore/ignore_test.go
@@ -25,7 +25,8 @@ import (
 )
 
 func TestIgnore(t *testing.T) {
-	pats, err := Load("testdata/.stignore", true)
+	pats := New(true)
+	err := pats.Load("testdata/.stignore")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -74,7 +75,8 @@ func TestExcludes(t *testing.T) {
 	i*2
 	!ign2
 	`
-	pats, err := Parse(bytes.NewBufferString(stignore), ".stignore")
+	pats := New(true)
+	err := pats.Parse(bytes.NewBufferString(stignore), ".stignore")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -114,15 +116,19 @@ func TestBadPatterns(t *testing.T) {
 	}
 
 	for _, pat := range badPatterns {
-		parsed, err := Parse(bytes.NewBufferString(pat), ".stignore")
+		err := New(true).Parse(bytes.NewBufferString(pat), ".stignore")
 		if err == nil {
-			t.Errorf("No error for pattern %q: %v", pat, parsed)
+			t.Errorf("No error for pattern %q", pat)
 		}
 	}
 }
 
 func TestCaseSensitivity(t *testing.T) {
-	ign, _ := Parse(bytes.NewBufferString("test"), ".stignore")
+	ign := New(true)
+	err := ign.Parse(bytes.NewBufferString("test"), ".stignore")
+	if err != nil {
+		t.Error(err)
+	}
 
 	match := []string{"test"}
 	dontMatch := []string{"foo"}
@@ -170,7 +176,8 @@ func TestCaching(t *testing.T) {
 
 	fd2.WriteString("/y/\n")
 
-	pats, err := Load(fd1.Name(), true)
+	pats := New(true)
+	err = pats.Load(fd1.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -193,9 +200,9 @@ func TestCaching(t *testing.T) {
 		t.Fatal("Expected 4 cached results")
 	}
 
-	// Reload file, expect old outcomes to be provided
+	// Reload file, expect old outcomes to be preserved
 
-	pats, err = Load(fd1.Name(), true)
+	err = pats.Load(fd1.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -207,7 +214,7 @@ func TestCaching(t *testing.T) {
 
 	fd2.WriteString("/z/\n")
 
-	pats, err = Load(fd1.Name(), true)
+	err = pats.Load(fd1.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -222,9 +229,9 @@ func TestCaching(t *testing.T) {
 		pats.Match(letter)
 	}
 
-	// Verify that outcomes provided on next laod
+	// Verify that outcomes preserved on next laod
 
-	pats, err = Load(fd1.Name(), true)
+	err = pats.Load(fd1.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -236,7 +243,7 @@ func TestCaching(t *testing.T) {
 
 	fd1.WriteString("/a/\n")
 
-	pats, err = Load(fd1.Name(), true)
+	err = pats.Load(fd1.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -252,7 +259,7 @@ func TestCaching(t *testing.T) {
 
 	// Verify that outcomes provided on next laod
 
-	pats, err = Load(fd1.Name(), true)
+	err = pats.Load(fd1.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -273,7 +280,11 @@ func TestCommentsAndBlankLines(t *testing.T) {
 
 
 	`
-	pats, _ := Parse(bytes.NewBufferString(stignore), ".stignore")
+	pats := New(true)
+	err := pats.Parse(bytes.NewBufferString(stignore), ".stignore")
+	if err != nil {
+		t.Error(err)
+	}
 	if len(pats.patterns) > 0 {
 		t.Errorf("Expected no patterns")
 	}
@@ -297,7 +308,11 @@ flamingo
 *.crow
 *.crow
 	`
-	pats, _ := Parse(bytes.NewBufferString(stignore), ".stignore")
+	pats := New(false)
+	err := pats.Parse(bytes.NewBufferString(stignore), ".stignore")
+	if err != nil {
+		b.Error(err)
+	}
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -335,7 +350,8 @@ flamingo
 	}
 
 	// Load the patterns
-	pats, err := Load(fd.Name(), true)
+	pats := New(true)
+	err = pats.Load(fd.Name())
 	if err != nil {
 		b.Fatal(err)
 	}
@@ -344,7 +360,7 @@ flamingo
 
 	// This load should now load the cached outcomes as the set of patterns
 	// has not changed.
-	pats, err = Load(fd.Name(), true)
+	err = pats.Load(fd.Name())
 	if err != nil {
 		b.Fatal(err)
 	}
@@ -370,7 +386,8 @@ func TestCacheReload(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	pats, err := Load(fd.Name(), true)
+	pats := New(true)
+	err = pats.Load(fd.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -402,7 +419,7 @@ func TestCacheReload(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	pats, err = Load(fd.Name(), true)
+	err = pats.Load(fd.Name())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -419,3 +436,85 @@ func TestCacheReload(t *testing.T) {
 		t.Error("Unexpected non-match for f3")
 	}
 }
+
+func TestHash(t *testing.T) {
+	p1 := New(true)
+	err := p1.Load("testdata/.stignore")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Same list of patterns as testdata/.stignore, after expansion
+	stignore := `
+	dir2/dfile
+	dir3
+	bfile
+	dir1/cfile
+	**/efile
+	/ffile
+	lost+found
+	`
+	p2 := New(true)
+	err = p2.Parse(bytes.NewBufferString(stignore), ".stignore")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Not same list of patterns
+	stignore = `
+	dir2/dfile
+	dir3
+	bfile
+	dir1/cfile
+	/ffile
+	lost+found
+	`
+	p3 := New(true)
+	err = p3.Parse(bytes.NewBufferString(stignore), ".stignore")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if p1.Hash() == "" {
+		t.Error("p1 hash blank")
+	}
+	if p2.Hash() == "" {
+		t.Error("p2 hash blank")
+	}
+	if p3.Hash() == "" {
+		t.Error("p3 hash blank")
+	}
+	if p1.Hash() != p2.Hash() {
+		t.Error("p1-p2 hashes differ")
+	}
+	if p1.Hash() == p3.Hash() {
+		t.Error("p1-p3 hashes same")
+	}
+}
+
+func TestHashOfEmpty(t *testing.T) {
+	p1 := New(true)
+	err := p1.Load("testdata/.stignore")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	firstHash := p1.Hash()
+
+	// Reloading with a non-existent file should empty the patterns and
+	// recalculate the hash. d41d8cd98f00b204e9800998ecf8427e is the md5 of
+	// nothing.
+
+	p1.Load("file/does/not/exist")
+	secondHash := p1.Hash()
+
+	if firstHash == secondHash {
+		t.Error("hash did not change")
+	}
+	if secondHash != "d41d8cd98f00b204e9800998ecf8427e" {
+		t.Error("second hash is not hash of empty string")
+	}
+	if len(p1.patterns) != 0 {
+		t.Error("there are more than zero patterns")
+	}
+}
diff --git a/internal/model/model.go b/internal/model/model.go
index 9ab9a8db4..fa9f143f0 100644
--- a/internal/model/model.go
+++ b/internal/model/model.go
@@ -1040,7 +1040,8 @@ func (m *Model) AddFolder(cfg config.FolderConfiguration) {
 		m.deviceFolders[device.DeviceID] = append(m.deviceFolders[device.DeviceID], cfg.ID)
 	}
 
-	ignores, _ := ignore.Load(filepath.Join(cfg.Path, ".stignore"), m.cfg.Options().CacheIgnoredFiles)
+	ignores := ignore.New(m.cfg.Options().CacheIgnoredFiles)
+	_ = ignores.Load(filepath.Join(cfg.Path, ".stignore")) // Ignore error, there might not be an .stignore
 	m.folderIgnores[cfg.ID] = ignores
 
 	m.addedFolder = true
@@ -1083,8 +1084,8 @@ func (m *Model) ScanFolderSub(folder, sub string) error {
 	fs, ok := m.folderFiles[folder]
 	dir := m.folderCfgs[folder].Path
 
-	ignores, _ := ignore.Load(filepath.Join(dir, ".stignore"), m.cfg.Options().CacheIgnoredFiles)
-	m.folderIgnores[folder] = ignores
+	ignores := m.folderIgnores[folder]
+	_ = ignores.Load(filepath.Join(dir, ".stignore")) // Ignore error, there might not be an .stignore
 
 	w := &scanner.Walker{
 		Dir:          dir,
diff --git a/internal/scanner/walk_test.go b/internal/scanner/walk_test.go
index 859b81d6b..f01d3232c 100644
--- a/internal/scanner/walk_test.go
+++ b/internal/scanner/walk_test.go
@@ -58,7 +58,8 @@ func init() {
 }
 
 func TestWalkSub(t *testing.T) {
-	ignores, err := ignore.Load("testdata/.stignore", false)
+	ignores := ignore.New(false)
+	err := ignores.Load("testdata/.stignore")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -93,7 +94,8 @@ func TestWalkSub(t *testing.T) {
 }
 
 func TestWalk(t *testing.T) {
-	ignores, err := ignore.Load("testdata/.stignore", false)
+	ignores := ignore.New(false)
+	err := ignores.Load("testdata/.stignore")
 	if err != nil {
 		t.Fatal(err)
 	}