src/path/filepath/path.go      | 32 ++++++++++++++++++++------------
 src/path/filepath/path_test.go |  4 ++++

diff --git a/src/path/filepath/path.go b/src/path/filepath/path.go
index 32dd887998650bff7cff4456c1ea1e023fcaa522..326ca006b2452904c944fa418c9619ce513fa3e1 100644
--- a/src/path/filepath/path.go
+++ b/src/path/filepath/path.go
@@ -52,6 +52,11 @@ 	b.buf[b.w] = c
 	b.w++
 }
 
+func (b *lazybuf) prepend(prefix ...byte) {
+	b.buf = append(prefix, b.buf...)
+	b.w += len(prefix)
+}
+
 func (b *lazybuf) string() string {
 	if b.buf == nil {
 		return b.volAndPath[:b.volLen+b.w]
@@ -146,18 +151,6 @@ 			// add slash if needed
 			if rooted && out.w != 1 || !rooted && out.w != 0 {
 				out.append(Separator)
 			}
-			// If a ':' appears in the path element at the start of a Windows path,
-			// insert a .\ at the beginning to avoid converting relative paths
-			// like a/../c: into c:.
-			if runtime.GOOS == "windows" && out.w == 0 && out.volLen == 0 && r != 0 {
-				for i := r; i < n && !os.IsPathSeparator(path[i]); i++ {
-					if path[i] == ':' {
-						out.append('.')
-						out.append(Separator)
-						break
-					}
-				}
-			}
 			// copy element
 			for ; r < n && !os.IsPathSeparator(path[r]); r++ {
 				out.append(path[r])
@@ -168,6 +161,21 @@
 	// Turn empty string into "."
 	if out.w == 0 {
 		out.append('.')
+	}
+
+	if runtime.GOOS == "windows" && out.volLen == 0 && out.buf != nil {
+		// If a ':' appears in the path element at the start of a Windows path,
+		// insert a .\ at the beginning to avoid converting relative paths
+		// like a/../c: into c:.
+		for _, c := range out.buf {
+			if os.IsPathSeparator(c) {
+				break
+			}
+			if c == ':' {
+				out.prepend('.', Separator)
+				break
+			}
+		}
 	}
 
 	return FromSlash(out.string())
diff --git a/src/path/filepath/path_test.go b/src/path/filepath/path_test.go
index 697bcc672d73c300482e335eeee3523cd82721a8..1a2e53a795a9f710e2833a7e26bca80418b1b839 100644
--- a/src/path/filepath/path_test.go
+++ b/src/path/filepath/path_test.go
@@ -66,6 +66,7 @@ 	{"abc/def/../../..", ".."},
 	{"/abc/def/../../..", "/"},
 	{"abc/def/../../../ghi/jkl/../../../mno", "../../mno"},
 	{"/../abc", "/abc"},
+	{"a/../b:/../../c", `../c`},
 
 	// Combinations
 	{"abc/./../def", "def"},
@@ -88,6 +89,7 @@ 	{`c:abc\..\..\.\.\..\def`, `c:..\..\def`},
 	{`c:\abc\def\..\..`, `c:\`},
 	{`c:\..\abc`, `c:\abc`},
 	{`c:..\abc`, `c:..\abc`},
+	{`c:\b:\..\..\..\d`, `c:\d`},
 	{`\`, `\`},
 	{`/`, `\`},
 	{`\\i\..\c$`, `\\i\..\c$`},
@@ -168,6 +170,7 @@ 	{"a/../a", true},
 	{"a/", true},
 	{"a/.", true},
 	{"a/./b/./c", true},
+	{`a/../b:/../../c`, false},
 }
 
 var winislocaltests = []IsLocalTest{
@@ -379,6 +382,7 @@ 	{[]string{`\`, `\\a\b`, `c`}, `\a\b\c`},
 	{[]string{`\\a`, `b`, `c`}, `\\a\b\c`},
 	{[]string{`\\a\`, `b`, `c`}, `\\a\b\c`},
 	{[]string{`//`, `a`}, `\\a`},
+	{[]string{`a:\b\c`, `x\..\y:\..\..\z`}, `a:\b\z`},
 }
 
 func TestJoin(t *testing.T) {