diff --git a/mongo/address/addr.go b/mongo/address/addr.go
index fb6abbcd7c..94f2fa0ba2 100644
--- a/mongo/address/addr.go
+++ b/mongo/address/addr.go
@@ -29,8 +29,7 @@ func (a Address) Network() string {
 // String is the canonical version of this address, e.g. localhost:27017,
 // 1.2.3.4:27017, example.com:27017.
 func (a Address) String() string {
-	// TODO: unicode case folding?
-	s := strings.ToLower(string(a))
+	s := string(a)
 	if len(s) == 0 {
 		return ""
 	}
diff --git a/mongo/address/addr_test.go b/mongo/address/addr_test.go
index 2242b6d49c..aeb2560500 100644
--- a/mongo/address/addr_test.go
+++ b/mongo/address/addr_test.go
@@ -18,8 +18,8 @@ func TestAddress_String(t *testing.T) {
 		expected string
 	}{
 		{"a", "a:27017"},
-		{"A", "a:27017"},
-		{"A:27017", "a:27017"},
+		{"A", "A:27017"},
+		{"A:27017", "A:27017"},
 		{"a:27017", "a:27017"},
 		{"a.sock", "a.sock"},
 	}
@@ -37,8 +37,8 @@ func TestAddress_Canonicalize(t *testing.T) {
 		expected string
 	}{
 		{"a", "a:27017"},
-		{"A", "a:27017"},
-		{"A:27017", "a:27017"},
+		{"A", "A:27017"},
+		{"A:27017", "A:27017"},
 		{"a:27017", "a:27017"},
 		{"a.sock", "a.sock"},
 	}