diff --git a/compiler/src/dotty/tools/dotc/core/classfile/ReusableDataReader.scala b/compiler/src/dotty/tools/dotc/core/classfile/ReusableDataReader.scala
index 35716feb7a42..3de211d4c0c6 100644
--- a/compiler/src/dotty/tools/dotc/core/classfile/ReusableDataReader.scala
+++ b/compiler/src/dotty/tools/dotc/core/classfile/ReusableDataReader.scala
@@ -35,47 +35,15 @@ final class ReusableDataReader() extends DataReader {
 
   def reset(file: dotty.tools.io.AbstractFile): this.type = {
     this.size = 0
-    file.sizeOption match {
-      case Some(size) =>
-        if (size > data.length) {
-          data = new Array[Byte](nextPositivePowerOfTwo(size))
-        } else {
-          java.util.Arrays.fill(data, 0.toByte)
-        }
-        val input = file.input
-        try {
-          var endOfInput = false
-          while (!endOfInput) {
-            val remaining = data.length - this.size
-            if (remaining == 0) endOfInput = true
-            else {
-              val read = input.read(data, this.size, remaining)
-              if (read < 0) endOfInput = true
-              else this.size += read
-            }
-          }
-          bb = ByteBuffer.wrap(data, 0, size)
-        } finally {
-          input.close()
-        }
-      case None =>
-        val input = file.input
-        try {
-          var endOfInput = false
-          while (!endOfInput) {
-            val remaining = data.length - size
-            if (remaining == 0) {
-              data = java.util.Arrays.copyOf(data, nextPositivePowerOfTwo(size))
-            }
-            val read = input.read(data, this.size, data.length - this.size)
-            if (read < 0) endOfInput = true
-            else this.size += read
-          }
-          bb = ByteBuffer.wrap(data, 0, size)
-        } finally {
-          input.close()
-        }
+    val bytes = file.toByteArray
+    val size = bytes.length
+    if (size > data.length) {
+      data = new Array[Byte](nextPositivePowerOfTwo(size))
+    } else {
+      java.util.Arrays.fill(data, 0.toByte)
     }
+    System.arraycopy(bytes, 0, data, 0, size)
+    bb = ByteBuffer.wrap(data, 0, size)
     this
   }
 
diff --git a/compiler/src/dotty/tools/io/AbstractFile.scala b/compiler/src/dotty/tools/io/AbstractFile.scala
index 69c4912886d1..d63f967ac270 100644
--- a/compiler/src/dotty/tools/io/AbstractFile.scala
+++ b/compiler/src/dotty/tools/io/AbstractFile.scala
@@ -55,6 +55,20 @@ object AbstractFile {
     else new PlainFile(new Path(Paths.get(url.toURI)))
 
   def getResources(url: URL): AbstractFile = ZipArchive.fromManifestURL(url)
+
+  val cache = scala.collection.mutable.Map[String, (Long, Array[Byte])]()
+  inline def cachedBytes(file: AbstractFile)(compute: => Array[Byte]): Array[Byte] = {
+    val key = file.absolutePath
+    val lastModified = file.lastModified
+    cache.get(key) match {
+      case Some((modTime, bytes)) if modTime == lastModified =>
+        bytes
+      case _ =>
+        val bytes = compute
+        cache.update(key, (lastModified, bytes))
+        bytes
+    }
+  }
 }
 
 /**
@@ -169,7 +183,7 @@ abstract class AbstractFile extends Iterable[AbstractFile] {
   /** Returns contents of file (if applicable) in a byte array.
    */
   @throws(classOf[IOException])
-  def toByteArray: Array[Byte] = {
+  def toByteArray: Array[Byte] = AbstractFile.cachedBytes(this) {
     val in = input
     sizeOption match {
       case Some(size) =>