diff --git a/aws/awsutil/strings.go b/aws/awsutil/strings.go
deleted file mode 100644
index 93bb091b502..00000000000
--- a/aws/awsutil/strings.go
+++ /dev/null
@@ -1,67 +0,0 @@
-package awsutil
-
-import (
-	"unicode"
-	"unicode/utf8"
-)
-
-// StringHasPrefixFold tests whether the string s begins with prefix, interpreted as UTF-8 strings,
-// under Unicode case-folding.
-//
-// This implementation is a modified version of the Go Standard Library's strings.EqualFold
-// Copyright 2009 The Go Authors. All rights reserved.
-func StringHasPrefixFold(s, prefix string) bool {
-	for s != "" && prefix != "" {
-		// Extract first rune from each string.
-		var sr, tr rune
-		if s[0] < utf8.RuneSelf {
-			sr, s = rune(s[0]), s[1:]
-		} else {
-			r, size := utf8.DecodeRuneInString(s)
-			sr, s = r, s[size:]
-		}
-		if prefix[0] < utf8.RuneSelf {
-			tr, prefix = rune(prefix[0]), prefix[1:]
-		} else {
-			r, size := utf8.DecodeRuneInString(prefix)
-			tr, prefix = r, prefix[size:]
-		}
-
-		// If they match, keep going; if not, return false.
-
-		// Easy case.
-		if tr == sr {
-			continue
-		}
-
-		// Make sr < tr to simplify what follows.
-		if tr < sr {
-			tr, sr = sr, tr
-		}
-		// Fast check for ASCII.
-		if tr < utf8.RuneSelf {
-			// ASCII only, sr/tr must be upper/lower case
-			if 'A' <= sr && sr <= 'Z' && tr == sr+'a'-'A' {
-				continue
-			}
-			return false
-		}
-
-		// General case. SimpleFold(x) returns the next equivalent rune > x
-		// or wraps around to smaller values.
-		r := unicode.SimpleFold(sr)
-		for r != sr && r < tr {
-			r = unicode.SimpleFold(r)
-		}
-		if r == tr {
-			continue
-		}
-		return false
-	}
-
-	if len(s) == 0 && len(prefix) > 0 {
-		return false
-	}
-
-	return true
-}
diff --git a/aws/signer/v4/header_rules.go b/aws/signer/v4/header_rules.go
index 11ef095a428..07ea799fbd3 100644
--- a/aws/signer/v4/header_rules.go
+++ b/aws/signer/v4/header_rules.go
@@ -1,7 +1,7 @@
 package v4
 
 import (
-	"github.com/aws/aws-sdk-go/aws/awsutil"
+	"github.com/aws/aws-sdk-go/internal/strings"
 )
 
 // validator houses a set of rule needed for validation of a
@@ -60,7 +60,7 @@ type patterns []string
 // been found
 func (p patterns) IsValid(value string) bool {
 	for _, pattern := range p {
-		if awsutil.StringHasPrefixFold(value, pattern) {
+		if strings.HasPrefixFold(value, pattern) {
 			return true
 		}
 	}
diff --git a/internal/strings/strings.go b/internal/strings/strings.go
new file mode 100644
index 00000000000..d008ae27cb3
--- /dev/null
+++ b/internal/strings/strings.go
@@ -0,0 +1,11 @@
+package strings
+
+import (
+	"strings"
+)
+
+// HasPrefixFold tests whether the string s begins with prefix, interpreted as UTF-8 strings,
+// under Unicode case-folding.
+func HasPrefixFold(s, prefix string) bool {
+	return len(s) >= len(prefix) && strings.EqualFold(s[0:len(prefix)], prefix)
+}
diff --git a/aws/awsutil/strings_test.go b/internal/strings/strings_test.go
similarity index 73%
rename from aws/awsutil/strings_test.go
rename to internal/strings/strings_test.go
index 35de34fefee..34d1769487f 100644
--- a/aws/awsutil/strings_test.go
+++ b/internal/strings/strings_test.go
@@ -1,13 +1,13 @@
 // +build go1.7
 
-package awsutil
+package strings
 
 import (
 	"strings"
 	"testing"
 )
 
-func TestStringPrefixFold(t *testing.T) {
+func TestHasPrefixFold(t *testing.T) {
 	type args struct {
 		s      string
 		prefix string
@@ -57,18 +57,25 @@ func TestStringPrefixFold(t *testing.T) {
 			},
 			want: true,
 		},
+		"mixed-case prefixes": {
+			args: args{
+				s:      "SoMe String",
+				prefix: "sOme",
+			},
+			want: true,
+		},
 	}
 	for name, tt := range tests {
 		t.Run(name, func(t *testing.T) {
-			if got := StringHasPrefixFold(tt.args.s, tt.args.prefix); got != tt.want {
-				t.Errorf("StringHasPrefixFold() = %v, want %v", got, tt.want)
+			if got := HasPrefixFold(tt.args.s, tt.args.prefix); got != tt.want {
+				t.Errorf("HasPrefixFold() = %v, want %v", got, tt.want)
 			}
 		})
 	}
 }
 
-func BenchmarkStringHasPrefixFold(b *testing.B) {
-	StringHasPrefixFold("SoME string", "sOmE")
+func BenchmarkHasPrefixFold(b *testing.B) {
+	HasPrefixFold("SoME string", "sOmE")
 }
 
 func BenchmarkHasPrefix(b *testing.B) {
diff --git a/private/protocol/rest/rest_test.go b/private/protocol/rest/rest_test.go
index 5902bcc50d8..58ed85abf0b 100644
--- a/private/protocol/rest/rest_test.go
+++ b/private/protocol/rest/rest_test.go
@@ -1,3 +1,5 @@
+// +build go1.7
+
 package rest_test
 
 import (
diff --git a/private/protocol/rest/unmarshal.go b/private/protocol/rest/unmarshal.go
index e947ecc68f4..f5f4530aba4 100644
--- a/private/protocol/rest/unmarshal.go
+++ b/private/protocol/rest/unmarshal.go
@@ -14,8 +14,8 @@ import (
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/awserr"
-	"github.com/aws/aws-sdk-go/aws/awsutil"
 	"github.com/aws/aws-sdk-go/aws/request"
+	awsStrings "github.com/aws/aws-sdk-go/internal/strings"
 	"github.com/aws/aws-sdk-go/private/protocol"
 )
 
@@ -154,7 +154,7 @@ func unmarshalHeaderMap(r reflect.Value, headers http.Header, prefix string, nor
 	case map[string]*string: // we only support string map value types
 		out := map[string]*string{}
 		for k, v := range headers {
-			if awsutil.StringHasPrefixFold(k, prefix) {
+			if awsStrings.HasPrefixFold(k, prefix) {
 				if normalize == true {
 					k = strings.ToLower(k)
 				} else {