diff --git a/aws/protocol/rest/encode_test.go b/aws/protocol/rest/encode_test.go
index 625d7962fba..63c69fc780c 100644
--- a/aws/protocol/rest/encode_test.go
+++ b/aws/protocol/rest/encode_test.go
@@ -21,8 +21,8 @@ func TestEncoder(t *testing.T) {
 	expected := http.Request{
 		Header: map[string][]string{
 			"custom-user-header": {"someValue"},
-			"x-amzn-header-foo":  {"someValue"},
-			"x-amzn-meta-foo":    {"someValue"},
+			"X-Amzn-Header-Foo":  {"someValue"},
+			"X-Amzn-Meta-Foo":    {"someValue"},
 		},
 		URL: &url.URL{
 			Path:     "/some/someValue/path",
diff --git a/aws/protocol/rest/header.go b/aws/protocol/rest/header.go
index 94917e969c0..ebf934b3dce 100644
--- a/aws/protocol/rest/header.go
+++ b/aws/protocol/rest/header.go
@@ -43,17 +43,11 @@ func newHeaderValue(header http.Header, key string, append bool) HeaderValue {
 }
 
 func (h HeaderValue) modifyHeader(value string) {
-	lk := strings.ToLower(h.key)
-
-	val := h.header[lk]
-
 	if h.append {
-		val = append(val, value)
+		h.header.Add(h.key, value)
 	} else {
-		val = append(val[:0], value)
+		h.header.Set(h.key, value)
 	}
-
-	h.header[lk] = val
 }
 
 // String encodes the value v as the header string value
diff --git a/aws/protocol/rest/header_test.go b/aws/protocol/rest/header_test.go
index db847eb2a99..f5ee99f8150 100644
--- a/aws/protocol/rest/header_test.go
+++ b/aws/protocol/rest/header_test.go
@@ -13,7 +13,7 @@ import (
 
 func TestHeaderValue(t *testing.T) {
 	const keyName = "test-key"
-	const expectedKeyName = keyName
+	const expectedKeyName = "Test-Key"
 
 	cases := map[string]struct {
 		header   http.Header
@@ -142,20 +142,20 @@ func TestHeaders(t *testing.T) {
 	}{
 		"set": {
 			headers: http.Header{
-				"x-amzn-meta-foo": {"bazValue"},
+				"X-Amzn-Meta-Foo": {"bazValue"},
 			},
 			values: map[string]string{
 				"foo":   "fooValue",
 				" bar ": "barValue",
 			},
 			expected: http.Header{
-				"x-amzn-meta-foo": {"fooValue"},
-				"x-amzn-meta-bar": {"barValue"},
+				"X-Amzn-Meta-Foo": {"fooValue"},
+				"X-Amzn-Meta-Bar": {"barValue"},
 			},
 		},
 		"add": {
 			headers: http.Header{
-				"x-amzn-meta-foo": {"bazValue"},
+				"X-Amzn-Meta-Foo": {"bazValue"},
 			},
 			values: map[string]string{
 				"foo":   "fooValue",
@@ -163,8 +163,8 @@ func TestHeaders(t *testing.T) {
 			},
 			append: true,
 			expected: http.Header{
-				"x-amzn-meta-foo": {"bazValue", "fooValue"},
-				"x-amzn-meta-bar": {"barValue"},
+				"X-Amzn-Meta-Foo": {"bazValue", "fooValue"},
+				"X-Amzn-Meta-Bar": {"barValue"},
 			},
 		},
 	}