2 files changed, 33 insertions, 2 deletions
diff --git a/src/main/scala/firrtl/options/phases/WriteOutputAnnotations.scala b/src/main/scala/firrtl/options/phases/WriteOutputAnnotations.scala
index 53306c8a..e9a39c67 100644
--- a/src/main/scala/firrtl/options/phases/WriteOutputAnnotations.scala
+++ b/src/main/scala/firrtl/options/phases/WriteOutputAnnotations.scala
@@ -6,7 +6,7 @@ import firrtl.AnnotationSeq
 import firrtl.annotations.{Annotation, DeletedAnnotation, JsonProtocol}
 import firrtl.options.{CustomFileEmission, Dependency, Phase, PhaseException, StageOptions, Unserializable, Viewer}
 
-import java.io.{BufferedWriter, File, FileWriter, PrintWriter}
+import java.io.{File, FileOutputStream, PrintWriter}
 
 import scala.collection.mutable
 
@@ -37,7 +37,7 @@ class WriteOutputAnnotations extends Phase {
 
         filesWritten.get(canonical) match {
           case None =>
-            val w = new BufferedWriter(new FileWriter(filename))
+            val w = new FileOutputStream(filename)
             a.getBytes.foreach(w.write(_))
             w.close()
             filesWritten(canonical) = a
diff --git a/src/test/scala/firrtlTests/options/phases/WriteOutputAnnotationsSpec.scala b/src/test/scala/firrtlTests/options/phases/WriteOutputAnnotationsSpec.scala
index 4fe16041..9e58585c 100644
--- a/src/test/scala/firrtlTests/options/phases/WriteOutputAnnotationsSpec.scala
+++ b/src/test/scala/firrtlTests/options/phases/WriteOutputAnnotationsSpec.scala
@@ -142,6 +142,28 @@ class WriteOutputAnnotationsSpec extends AnyFlatSpec with Matchers with firrtl.t
     new File(serializedFileName) should (exist)
   }
 
+  it should "support CustomFileEmission to binary files" in new Fixture {
+    val file = new File("write-CustomFileEmission-binary-files.anno.json")
+    val data = Array[Byte](0x0a, 0xa0.toByte)
+    val annotations = Seq(
+      TargetDirAnnotation(dir),
+      OutputAnnotationFileAnnotation(file.toString),
+      WriteOutputAnnotationsSpec.Binary(data)
+    )
+
+    val serializedFileName = view[StageOptions](annotations).getBuildFileName("Binary", Some(".Emission"))
+    val out = phase.transform(annotations)
+
+    info(s"file '$serializedFileName' exists")
+    new File(serializedFileName) should (exist)
+
+    info(s"file '$serializedFileName' is correct")
+    val inputStream = new java.io.FileInputStream(serializedFileName)
+    val result = new Array[Byte](2)
+    inputStream.read(result)
+    result should equal(data)
+  }
+
   it should "error if multiple annotations try to write to the same file" in new Fixture {
     val file = new File("write-CustomFileEmission-annotations-error.anno.json")
     val annotations = Seq(
@@ -175,6 +197,15 @@ private object WriteOutputAnnotationsSpec {
 
   }
 
+  case class Binary(value: Array[Byte]) extends NoTargetAnnotation with CustomFileEmission {
+
+    override protected def baseFileName(a: AnnotationSeq): String = "Binary"
+
+    override protected def suffix: Option[String] = Some(".Emission")
+
+    override def getBytes: Iterable[Byte] = value
+  }
+
   case class Replacement(file: String) extends NoTargetAnnotation
 
 }