diff --git a/internal/zinc-classfile/src/main/scala/sbt/internal/inc/classfile/Parser.scala b/internal/zinc-classfile/src/main/scala/sbt/internal/inc/classfile/Parser.scala
index edbc7c3da..28f560a00 100644
--- a/internal/zinc-classfile/src/main/scala/sbt/internal/inc/classfile/Parser.scala
+++ b/internal/zinc-classfile/src/main/scala/sbt/internal/inc/classfile/Parser.scala
@@ -39,13 +39,13 @@ import Constants._
 private[sbt] object Parser {
 
   def apply(file: Path, log: Logger): ClassFile =
-    Using.bufferedInputStream(Files.newInputStream(file))(parse(file.toString, log)).right.get
+    Using.bufferedInputStream(Files.newInputStream(file))(parse(file.toString, log)).toOption.get
 
   def apply(file: File, log: Logger): ClassFile =
-    Using.fileInputStream(file)(parse(file.toString, log)).right.get
+    Using.fileInputStream(file)(parse(file.toString, log)).toOption.get
 
   def apply(url: URL, log: Logger): ClassFile =
-    usingUrlInputStreamWithoutCaching(url)(parse(url.toString, log)).right.get
+    usingUrlInputStreamWithoutCaching(url)(parse(url.toString, log)).toOption.get
 
   // JarURLConnection with caching enabled will never close the jar
   private val usingUrlInputStreamWithoutCaching = Using.resource((u: URL) =>
diff --git a/internal/zinc-classpath/src/main/scala/sbt/internal/inc/ReflectUtilities.scala b/internal/zinc-classpath/src/main/scala/sbt/internal/inc/ReflectUtilities.scala
index 61f376182..86e74afaa 100644
--- a/internal/zinc-classpath/src/main/scala/sbt/internal/inc/ReflectUtilities.scala
+++ b/internal/zinc-classpath/src/main/scala/sbt/internal/inc/ReflectUtilities.scala
@@ -36,7 +36,7 @@ object ReflectUtilities {
     else clazz :: ancestry(clazz.getSuperclass);
 
   def fields(clazz: Class[?]) =
-    mutable.OpenHashMap(ancestry(clazz).flatMap(_.getDeclaredFields).map(f => (f.getName, f)): _*)
+    mutable.AnyRefMap(ancestry(clazz).flatMap(_.getDeclaredFields).map(f => (f.getName, f)): _*)
 
   /**
    * Collects all `val`s of type `T` defined on value `self`.
diff --git a/internal/zinc-classpath/src/main/scala/sbt/internal/inc/classpath/ClassLoaders.scala b/internal/zinc-classpath/src/main/scala/sbt/internal/inc/classpath/ClassLoaders.scala
index 3074c2d23..fde68b471 100644
--- a/internal/zinc-classpath/src/main/scala/sbt/internal/inc/classpath/ClassLoaders.scala
+++ b/internal/zinc-classpath/src/main/scala/sbt/internal/inc/classpath/ClassLoaders.scala
@@ -191,8 +191,8 @@ trait NativeCopyLoader extends ClassLoader {
 
   private[this] def findLibrary0(name: String): String = {
     val mappedName = System.mapLibraryName(name)
-    val explicit = explicitLibraries.toIterator.filter(_.getFileName.toString == mappedName)
-    val search = searchPaths.toIterator flatMap relativeLibrary(mappedName)
+    val explicit = explicitLibraries.iterator.filter(_.getFileName.toString == mappedName)
+    val search = searchPaths.iterator flatMap relativeLibrary(mappedName)
     val combined = explicit ++ search
     if (combined.hasNext) copy(combined.next()) else null
   }
diff --git a/internal/zinc-core/src/main/scala/sbt/internal/inc/Compilations.scala b/internal/zinc-core/src/main/scala/sbt/internal/inc/Compilations.scala
index b8021a66b..f992ee7fb 100644
--- a/internal/zinc-core/src/main/scala/sbt/internal/inc/Compilations.scala
+++ b/internal/zinc-core/src/main/scala/sbt/internal/inc/Compilations.scala
@@ -30,7 +30,7 @@ trait Compilations extends ReadCompilations {
 object Compilations {
   val empty: Compilations = new MCompilations(Seq.empty)
   def of(s: Seq[Compilation]): Compilations = new MCompilations(s)
-  def merge(s: Traversable[Compilations]): Compilations =
+  def merge(s: Iterable[Compilations]): Compilations =
     of((s flatMap { _.allCompilations }).toSeq.distinct)
 }
 
diff --git a/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/FormatCommons.scala b/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/FormatCommons.scala
index eef736e0a..20d28cd06 100644
--- a/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/FormatCommons.scala
+++ b/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/FormatCommons.scala
@@ -155,7 +155,7 @@ trait FormatCommons {
 
   protected def readMappedPairs[K, V](
       in: BufferedReader
-  )(expectedHeader: String, s2k: String => K, s2v: (K, String) => V): Traversable[(K, V)] = {
+  )(expectedHeader: String, s2k: String => K, s2v: (K, String) => V): Iterable[(K, V)] = {
     def toPair(s: String): (K, V) = {
       if (s == null) throw new EOFException
       val p = s.indexOf(" -> ")
diff --git a/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/RelationsTextFormat.scala b/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/RelationsTextFormat.scala
index eae0ced88..495b31008 100644
--- a/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/RelationsTextFormat.scala
+++ b/internal/zinc-persist/src/main/scala/sbt/internal/inc/text/RelationsTextFormat.scala
@@ -82,7 +82,7 @@ trait RelationsTextFormat extends FormatCommons {
     def read(in: BufferedReader): Relations = {
       def readRelation[A, B](relDesc: Descriptor[A, B]): Map[A, Set[B]] = {
         import relDesc._
-        val items = readPairs(in)(header, keyMapper.read, valueMapper.read).toIterator
+        val items = readPairs(in)(header, keyMapper.read, valueMapper.read).iterator
         // Reconstruct the multi-map efficiently, using the writing strategy above
         val builder = Map.newBuilder[A, Set[B]]
         var currentKey = null.asInstanceOf[A]