5 files changed, 71 insertions, 12 deletions
diff --git a/plumbing/format/config/decoder_test.go b/plumbing/format/config/decoder_test.go
index 412549f..0a8e92c 100644
--- a/plumbing/format/config/decoder_test.go
+++ b/plumbing/format/config/decoder_test.go
@@ -17,7 +17,10 @@ func (s *DecoderSuite) TestDecode(c *C) {
 		cfg := &Config{}
 		err := d.Decode(cfg)
 		c.Assert(err, IsNil, Commentf("decoder error for fixture: %d", idx))
-		c.Assert(cfg, DeepEquals, fixture.Config, Commentf("bad result for fixture: %d", idx))
+		buf := bytes.NewBuffer(nil)
+		e := NewEncoder(buf)
+		_ = e.Encode(cfg)
+		c.Assert(cfg, DeepEquals, fixture.Config, Commentf("bad result for fixture: %d, %s", idx, buf.String()))
 	}
 }
 
diff --git a/plumbing/format/config/fixtures_test.go b/plumbing/format/config/fixtures_test.go
index 12ff288..f3533df 100644
--- a/plumbing/format/config/fixtures_test.go
+++ b/plumbing/format/config/fixtures_test.go
@@ -87,4 +87,18 @@ var fixtures = []*Fixture{
 			AddOption("sect1", "subsect1", "opt2", "value2b").
 			AddOption("sect1", "subsect2", "opt2", "value2"),
 	},
+	{
+		Raw: `
+			[sect1]
+			opt1 = value1
+			opt1 = value2
+			`,
+		Text: `[sect1]
+	opt1 = value1
+	opt1 = value2
+`,
+		Config: New().
+			AddOption("sect1", "", "opt1", "value1").
+			AddOption("sect1", "", "opt1", "value2"),
+	},
 }
diff --git a/plumbing/format/config/option.go b/plumbing/format/config/option.go
index 481af02..d4775e4 100644
--- a/plumbing/format/config/option.go
+++ b/plumbing/format/config/option.go
@@ -79,16 +79,39 @@ func (opts Options) withAddedOption(key string, value string) Options {
 	return append(opts, &Option{key, value})
 }
 
-func (opts Options) withSettedOption(key string, value string) Options {
-	for i := len(opts) - 1; i >= 0; i-- {
-		o := opts[i]
-		if o.IsKey(key) {
-			result := make(Options, len(opts))
-			copy(result, opts)
-			result[i] = &Option{key, value}
-			return result
+func (opts Options) withSettedOption(key string, values ...string) Options {
+	var result Options
+	var added []string
+	for _, o := range opts {
+		if !o.IsKey(key) {
+			result = append(result, o)
+			continue
+		}
+
+		if contains(values, o.Value) {
+			added = append(added, o.Value)
+			result = append(result, o)
+			continue
+		}
+	}
+
+	for _, value := range values {
+		if contains(added, value) {
+			continue
+		}
+
+		result = result.withAddedOption(key, value)
+	}
+
+	return result
+}
+
+func contains(haystack []string, needle string) bool {
+	for _, s := range haystack {
+		if s == needle {
+			return true
 		}
 	}
 
-	return opts.withAddedOption(key, value)
+	return false
 }
diff --git a/plumbing/format/config/section.go b/plumbing/format/config/section.go
index eeefe84..4a17e3b 100644
--- a/plumbing/format/config/section.go
+++ b/plumbing/format/config/section.go
@@ -134,8 +134,8 @@ func (s *Subsection) AddOption(key string, value string) *Subsection {
 
 // SetOption adds a new Option to the Subsection. If the option already exists, is replaced.
 // The updated Subsection is returned.
-func (s *Subsection) SetOption(key string, value string) *Subsection {
-	s.Options = s.Options.withSettedOption(key, value)
+func (s *Subsection) SetOption(key string, value ...string) *Subsection {
+	s.Options = s.Options.withSettedOption(key, value...)
 	return s
 }
 
diff --git a/plumbing/format/config/section_test.go b/plumbing/format/config/section_test.go
index cfd9f3f..0290386 100644
--- a/plumbing/format/config/section_test.go
+++ b/plumbing/format/config/section_test.go
@@ -69,3 +69,22 @@ func (s *SectionSuite) TestSubsection_RemoveOption(c *C) {
 	}
 	c.Assert(sect.RemoveOption("key1"), DeepEquals, expected)
 }
+
+func (s *SectionSuite) TestSubsection_SetOption(c *C) {
+	sect := &Subsection{
+		Options: []*Option{
+			{Key: "key1", Value: "value1"},
+			{Key: "key2", Value: "value2"},
+			{Key: "key1", Value: "value3"},
+		},
+	}
+
+	expected := &Subsection{
+		Options: []*Option{
+			{Key: "key1", Value: "value1"},
+			{Key: "key2", Value: "value2"},
+			{Key: "key1", Value: "value4"},
+		},
+	}
+	c.Assert(sect.SetOption("key1", "value1", "value4"), DeepEquals, expected)
+}