diff --git a/vendor/modules.txt b/vendor/modules.txt
index 866473f9..2dea7837 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -38,7 +38,7 @@ golang.org/x/sys/unix
 golang.org/x/sys/windows
 # gopkg.in/yaml.v2 v2.2.1
 gopkg.in/yaml.v2
-# mvdan.cc/sh v2.6.3+incompatible
+# mvdan.cc/sh v2.6.4-0.20190222161105-3c71c7be1070+incompatible
 mvdan.cc/sh/expand
 mvdan.cc/sh/interp
 mvdan.cc/sh/shell
diff --git a/vendor/mvdan.cc/sh/expand/expand.go b/vendor/mvdan.cc/sh/expand/expand.go
index 633b43a7..16f63d45 100644
--- a/vendor/mvdan.cc/sh/expand/expand.go
+++ b/vendor/mvdan.cc/sh/expand/expand.go
@@ -373,7 +373,11 @@ func (cfg *Config) wordField(wps []syntax.WordPart, ql quoteLevel) ([]fieldPart,
 		case *syntax.Lit:
 			s := x.Value
 			if i == 0 && ql == quoteNone {
-				s = cfg.expandUser(s)
+				if prefix, rest := cfg.expandUser(s); prefix != "" {
+					// TODO: return two separate fieldParts,
+					// like in wordFields?
+					s = prefix + rest
+				}
 			}
 			if ql == quoteDouble && strings.Contains(s, "\\") {
 				buf := cfg.strBuilder()
@@ -468,7 +472,12 @@ func (cfg *Config) wordFields(wps []syntax.WordPart) ([][]fieldPart, error) {
 		case *syntax.Lit:
 			s := x.Value
 			if i == 0 {
-				s = cfg.expandUser(s)
+				prefix, rest := cfg.expandUser(s)
+				curField = append(curField, fieldPart{
+					quote: quoteSingle,
+					val:   prefix,
+				})
+				s = rest
 			}
 			if strings.Contains(s, "\\") {
 				buf := cfg.strBuilder()
@@ -562,28 +571,27 @@ func (cfg *Config) quotedElems(pe *syntax.ParamExp) []string {
 	return nil
 }
 
-func (cfg *Config) expandUser(field string) string {
+func (cfg *Config) expandUser(field string) (prefix, rest string) {
 	if len(field) == 0 || field[0] != '~' {
-		return field
+		return "", field
 	}
 	name := field[1:]
-	rest := ""
 	if i := strings.Index(name, "/"); i >= 0 {
 		rest = name[i:]
 		name = name[:i]
 	}
 	if name == "" {
-		return cfg.Env.Get("HOME").String() + rest
+		return cfg.Env.Get("HOME").String(), rest
 	}
 	if vr := cfg.Env.Get("HOME " + name); vr.IsSet() {
-		return vr.String() + rest
+		return vr.String(), rest
 	}
 
 	u, err := user.Lookup(name)
 	if err != nil {
-		return field
+		return "", field
 	}
-	return u.HomeDir + rest
+	return u.HomeDir, rest
 }
 
 func findAllIndex(pattern, name string, n int) [][]int {
diff --git a/vendor/mvdan.cc/sh/interp/interp.go b/vendor/mvdan.cc/sh/interp/interp.go
index b7ce7657..4a5a8b41 100644
--- a/vendor/mvdan.cc/sh/interp/interp.go
+++ b/vendor/mvdan.cc/sh/interp/interp.go
@@ -1182,6 +1182,10 @@ func (r *Runner) findExecutable(file string, exts []string) string {
 	return ""
 }
 
+func driveLetter(c byte) bool {
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+}
+
 // splitList is like filepath.SplitList, but always using the unix path
 // list separator ':'. On Windows, it also makes sure not to split
 // [A-Z]:[/\].
@@ -1198,8 +1202,7 @@ func splitList(path string) []string {
 	for i := 0; i < len(list); i++ {
 		s := list[i]
 		switch {
-		case len(s) != 1, s[0] < 'A', s[0] > 'Z':
-			// not a disk name
+		case len(s) != 1, !driveLetter(s[0]):
 		case i+1 >= len(list):
 			// last element
 		case strings.IndexAny(list[i+1], `/\`) != 0:
diff --git a/vendor/mvdan.cc/sh/interp/test.go b/vendor/mvdan.cc/sh/interp/test.go
index f5378433..96cc311b 100644
--- a/vendor/mvdan.cc/sh/interp/test.go
+++ b/vendor/mvdan.cc/sh/interp/test.go
@@ -19,7 +19,7 @@ import (
 func (r *Runner) bashTest(ctx context.Context, expr syntax.TestExpr, classic bool) string {
 	switch x := expr.(type) {
 	case *syntax.Word:
-		return r.literal(x)
+		return r.document(x)
 	case *syntax.ParenTest:
 		return r.bashTest(ctx, x.X, classic)
 	case *syntax.BinaryTest:
diff --git a/vendor/mvdan.cc/sh/shell/doc.go b/vendor/mvdan.cc/sh/shell/doc.go
index 695f233c..96ae5705 100644
--- a/vendor/mvdan.cc/sh/shell/doc.go
+++ b/vendor/mvdan.cc/sh/shell/doc.go
@@ -3,4 +3,12 @@
 
 // Package shell contains high-level features that use the syntax, expand, and
 // interp packages under the hood.
+//
+// Please note that this package uses POSIX Shell syntax. As such, path names on
+// Windows need to use double backslashes or be within single quotes when given
+// to functions like Fields. For example:
+//
+//     shell.Fields("echo /foo/bar")     // on Unix-like
+//     shell.Fields("echo C:\\foo\\bar") // on Windows
+//     shell.Fields("echo 'C:\foo\bar'") // on Windows, with quotes
 package shell