diff --git a/build.sbt b/build.sbt
index acf8d04..8693f75 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,20 +1,25 @@
 val Leaf       = "0.1.0"
 val Scala2_11  = "2.11.12"
-val Scala2_12  = "2.12.13"
-val Scala2_13  = "2.13.4"
-val ScalaTest  = "3.2.4-M1"
+val Scala2_12  = "2.12.15"
+val Scala2_13  = "2.13.8"
+val Scala3     = "3.1.1"
+val ScalaTest  = "3.2.12"
 
 val SharedSettings = Seq(
   name         := "trail",
   organization := "tech.sparse",
 
   scalaVersion       := Scala2_13,
-  crossScalaVersions := Seq(Scala2_13, Scala2_12, Scala2_11),
-  scalacOptions      := Seq(
-    "-unchecked",
-    "-deprecation",
-    "-encoding", "utf8"
-  ),
+  crossScalaVersions := Seq(Scala3, Scala2_13, Scala2_12, Scala2_11),
+  scalacOptions      := {
+    // Preserve -scalajs flag used by Scala.js on Scala 3
+    scalacOptions.value.filter(_ == "-scalajs") ++ 
+    Seq(
+      "-unchecked",
+      "-deprecation",
+      "-encoding", "utf8"
+    )
+  },
 
   pomExtra :=
     <url>https://github.com/sparsetech/trail</url>
@@ -60,3 +65,9 @@ lazy val manual = project.in(file("manual"))
     publishArtifact := false,
     libraryDependencies += "tech.sparse" %% "leaf-notebook" % Leaf
   )
+
+def isScala3(ver: String) = 
+  CrossVersion.partialVersion(ver) match {
+    case Some((3, _)) => true
+    case _ => false
+  }
diff --git a/native/src/main/scala/trail/URI.scala b/native/src/main/scala/trail/URI.scala
index 496bf40..f00d114 100644
--- a/native/src/main/scala/trail/URI.scala
+++ b/native/src/main/scala/trail/URI.scala
@@ -25,7 +25,7 @@ object URI {
       if (c == '+') result.append(' ')
       else if (c == '%') {
         out.reset()
-        do {
+        while({
           if (i + 2 >= s.length)
             throw new IllegalArgumentException("Incomplete % sequence at: " + i)
           val d1 = Character.digit(s.charAt(i + 1), 16)
@@ -35,7 +35,8 @@ object URI {
               s"Invalid % sequence (${s.substring(i, i + 3)}) at: ${String.valueOf(i)}.")
           out.write(((d1 << 4) + d2).toByte)
           i += 3
-        } while (i < s.length && s.charAt(i) == '%')
+          (i < s.length && s.charAt(i) == '%')
+        }) { }
         result.append(out.toString("UTF-8"))
       } else {
         result.append(c)
diff --git a/project/build.properties b/project/build.properties
index d91c272..c8fcab5 100644
--- a/project/build.properties
+++ b/project/build.properties
@@ -1 +1 @@
-sbt.version=1.4.6
+sbt.version=1.6.2
diff --git a/project/plugins.sbt b/project/plugins.sbt
index dfbeda3..d3405e6 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -2,5 +2,5 @@ logLevel := Level.Warn
 
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject"      % "1.0.0")
 addSbtPlugin("org.portable-scala" % "sbt-scala-native-crossproject" % "1.0.0")
-addSbtPlugin("org.scala-js"       % "sbt-scalajs"                   % "1.3.1")
-addSbtPlugin("org.scala-native"   % "sbt-scala-native"              % "0.4.0")
+addSbtPlugin("org.scala-js"       % "sbt-scalajs"                   % "1.9.0")
+addSbtPlugin("org.scala-native"   % "sbt-scala-native"              % "0.4.4")
diff --git a/shared/src/main/scala/trail/PathElement.scala b/shared/src/main/scala/trail/PathElement.scala
index 5af4b18..c0890b0 100644
--- a/shared/src/main/scala/trail/PathElement.scala
+++ b/shared/src/main/scala/trail/PathElement.scala
@@ -1,6 +1,6 @@
 package trail
 
-case class Arg[T]()(implicit val codec: Codec[T]) {
+class Arg[T]()(implicit val codec: Codec[T]) {
   override def equals(o: Any): Boolean =
     o match {
       case a: Arg[T] => a.codec.equals(codec)
@@ -10,6 +10,10 @@ case class Arg[T]()(implicit val codec: Codec[T]) {
   override def hashCode(): Int = ("trail.Arg", codec).hashCode()
 }
 
+object Arg {
+  def apply[T](implicit codec: Codec[T]) = new Arg()
+}
+
 case class Param[T](name: String)(implicit val codec: Codec[T]) {
   override def equals(o: Any): Boolean =
     o match {
@@ -20,7 +24,7 @@ case class Param[T](name: String)(implicit val codec: Codec[T]) {
   override def hashCode(): Int = ("trail.Param", name, codec).hashCode()
 }
 
-case class Fragment[T]()(implicit val codec: Codec[T]) {
+class Fragment[T](implicit val codec: Codec[T]) {
   override def equals(o: Any): Boolean =
     o match {
       case f: Fragment[T] => f.codec.equals(codec)
@@ -29,3 +33,7 @@ case class Fragment[T]()(implicit val codec: Codec[T]) {
 
   override def hashCode(): Int = ("trail.Fragment", codec).hashCode()
 }
+
+object Fragment {
+  def apply[T](implicit codec: Codec[T]) = new Fragment[T]
+}