diff --git a/formatter.go b/formatter.go
index bf4b598..f3718ea 100644
--- a/formatter.go
+++ b/formatter.go
@@ -8,6 +8,7 @@ import (
 	"text/tabwriter"
 
 	"github.com/kr/text"
+	"github.com/rogpeppe/go-internal/fmtsort"
 )
 
 type formatter struct {
@@ -123,10 +124,10 @@ func (p *printer) printValue(v reflect.Value, showType, quote bool) {
 				writeByte(p, '\n')
 				pp = p.indent()
 			}
-			keys := v.MapKeys()
+			sm := fmtsort.Sort(v)
 			for i := 0; i < v.Len(); i++ {
-				k := keys[i]
-				mv := v.MapIndex(k)
+				k := sm.Key[i]
+				mv := sm.Value[i]
 				pp.printValue(k, false, true)
 				writeByte(pp, ':')
 				if expand {
diff --git a/formatter_test.go b/formatter_test.go
index c8c0b51..10ce57a 100644
--- a/formatter_test.go
+++ b/formatter_test.go
@@ -38,7 +38,7 @@ func (f F) Format(s fmt.State, c rune) {
 	fmt.Fprintf(s, "F(%d)", int(f))
 }
 
-type Stringer struct { i int }
+type Stringer struct{ i int }
 
 func (s *Stringer) String() string { return "foo" }
 
@@ -74,6 +74,7 @@ var gosyntax = []test{
 	//{make(chan int), "(chan int)(0x1234)"},
 	{unsafe.Pointer(uintptr(unsafe.Pointer(&long))), fmt.Sprintf("unsafe.Pointer(0x%02x)", uintptr(unsafe.Pointer(&long)))},
 	{func(int) {}, "func(int) {...}"},
+	{map[string]string{"a": "a", "b": "b"}, "map[string]string{\"a\":\"a\", \"b\":\"b\"}"},
 	{map[int]int{1: 1}, "map[int]int{1:1}"},
 	{int32(1), "int32(1)"},
 	{io.EOF, `&errors.errorString{s:"EOF"}`},
diff --git a/go.mod b/go.mod
index 9a27b6e..579209a 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,7 @@ module github.com/kr/pretty
 
 go 1.12
 
-require github.com/kr/text v0.1.0
+require (
+	github.com/kr/text v0.1.0
+	github.com/rogpeppe/go-internal v1.6.1
+)
diff --git a/go.sum b/go.sum
index 714f82a..a0e55fc 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,8 @@
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/rogpeppe/go-internal v1.6.1 h1:/FiVV8dS/e+YqF2JvO3yXRFbBLTIuSDkuC7aBOAvL+k=
+github.com/rogpeppe/go-internal v1.6.1/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=