diff --git a/internal/fsutil/path.go b/internal/fsutil/path.go
new file mode 100644
index 00000000..15646e5e
--- /dev/null
+++ b/internal/fsutil/path.go
@@ -0,0 +1,47 @@
+package fsutil
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// These functions exists because we work with slash terminated directory paths
+// that come from deb package tarballs but standard library path functions
+// treat slash terminated paths as unclean.
+
+// Dir is like filepath.Dir() but trailing slash on input is ignored and the
+// return value always includes trailing slash.
+//
+// Comparison of filepath.Dir() with fsutil.Dir():
+//
+//	filepath.Dir("/foo/bar/")	== "/foo/bar"
+//	filepath.Dir("/foo/bar")	== "/foo"
+//
+//	fsutil.Dir("/foo/bar")		== "/foo/"
+//	fsutil.Dir("/foo/bar/")		== "/foo/"
+func Dir(path string) string {
+	parent := filepath.Dir(filepath.Clean(path))
+	if parent != "/" {
+		parent += "/"
+	}
+	return parent
+}
+
+// Clean is like filepath.Clean() but trailing slash is kept.
+//
+// Comparison of filepath.Clean() with fsutil.Clean():
+//
+//	filepath.Clean("/foo/bar")	== "/foo/bar"
+//	filepath.Clean("/foo/bar/")	== "/foo/bar"
+//	filepath.Clean("/foo/bar/.//)	== "/foo/bar"
+//
+//	fsutil.Clean("/foo/bar")	== "/foo/bar"
+//	fsutil.Clean("/foo/bar/")	== "/foo/bar/"
+//	fsutil.Clean("/foo/bar/.//")	== "/foo/bar/"
+func Clean(path string) string {
+	clean := filepath.Clean(path)
+	if strings.HasSuffix(path, "/") {
+		clean += "/"
+	}
+	return clean
+}
diff --git a/internal/fsutil/path_test.go b/internal/fsutil/path_test.go
new file mode 100644
index 00000000..9d39230c
--- /dev/null
+++ b/internal/fsutil/path_test.go
@@ -0,0 +1,52 @@
+package fsutil_test
+
+import (
+	. "gopkg.in/check.v1"
+
+	"github.com/canonical/chisel/internal/fsutil"
+)
+
+var dirTests = []struct {
+	input  string
+	output string
+}{
+	{"/a/b/c", "/a/b/"},
+	{"/a/b/c/", "/a/b/"},
+	{"/a/b/c//", "/a/b/"},
+	{"/a/b/c/././", "/a/b/"},
+	{"/a/b/c/.././", "/a/"},
+	{"/a/b//c", "/a/b/"},
+	{"/a/b/./c", "/a/b/"},
+	{"a/b/./c", "a/b/"},
+	{"./a/b/./c", "a/b/"},
+	{"/", "/"},
+	{"///.///", "/"},
+	{".", "./"},
+	{"", "./"},
+}
+
+var cleanTests = []struct {
+	input  string
+	output string
+}{
+	{"/a/b/c", "/a/b/c"},
+	{"/a/b/c/", "/a/b/c/"},
+	{"/a/b/c/.//", "/a/b/c/"},
+	{"/a/b//./c", "/a/b/c"},
+	{"/a/b//./c/", "/a/b/c/"},
+	{"/a/b/.././c/", "/a/c/"},
+}
+
+func (s *S) TestDir(c *C) {
+	for _, t := range dirTests {
+		c.Logf("%s => %s", t.input, t.output)
+		c.Assert(fsutil.Dir(t.input), Equals, t.output)
+	}
+}
+
+func (s *S) TestClean(c *C) {
+	for _, t := range cleanTests {
+		c.Logf("%s => %s", t.input, t.output)
+		c.Assert(fsutil.Clean(t.input), Equals, t.output)
+	}
+}
diff --git a/internal/slicer/slicer.go b/internal/slicer/slicer.go
index 2b684b5d..ea6b0b86 100644
--- a/internal/slicer/slicer.go
+++ b/internal/slicer/slicer.go
@@ -32,25 +32,21 @@ func Run(options *RunOptions) error {
 
 	knownPaths["/"] = true
 
+	// addKnownPath path adds path and all its directory parent paths into
+	// knownPaths set.
 	addKnownPath := func(path string) {
 		if path[0] != '/' {
 			panic("bug: tried to add relative path to known paths")
 		}
-		cleanPath := filepath.Clean(path)
-		slashPath := cleanPath
-		if path[len(path)-1] == '/' && cleanPath != "/" {
-			slashPath += "/"
-		}
+		path = fsutil.Clean(path)
 		for {
-			if _, ok := knownPaths[slashPath]; ok {
+			if _, ok := knownPaths[path]; ok {
 				break
 			}
-			knownPaths[slashPath] = true
-			cleanPath = filepath.Dir(cleanPath)
-			if cleanPath == "/" {
+			knownPaths[path] = true
+			if path = fsutil.Dir(path); path == "/" {
 				break
 			}
-			slashPath = cleanPath + "/"
 		}
 	}
 
@@ -113,7 +109,7 @@ func Run(options *RunOptions) error {
 					hasCopyright = true
 				}
 			} else {
-				targetDir := filepath.Dir(strings.TrimRight(targetPath, "/")) + "/"
+				targetDir := fsutil.Dir(targetPath)
 				if targetDir == "" || targetDir == "/" {
 					continue
 				}