diff --git a/core/src/main/scala/chisel3/Module.scala b/core/src/main/scala/chisel3/Module.scala
index 48c33083c91..e5c2a8488a4 100644
--- a/core/src/main/scala/chisel3/Module.scala
+++ b/core/src/main/scala/chisel3/Module.scala
@@ -106,6 +106,38 @@ object Module extends SourceInfoDoc {
 
     module
   }
+
+  /**  Assign directionality on any IOs that are still Unspecified/Flipped
+    *
+    *  Chisel2 did not require explicit direction on nodes
+    *  (unspecified treated as output, and flip on nothing was input).
+    *  As of 3.6, chisel3 is now also using these semantics, so we need to make it work
+    *  even for chisel3 code.
+    *  This assigns the explicit directions required by both semantics on all Bundles.
+    * This recursively walks the tree, and assigns directions if no explicit
+    *   direction given by upper-levels (override Input / Output)
+    */
+  private[chisel3] def assignCompatDir(data: Data): Unit = {
+    data match {
+      case data: Element => data._assignCompatibilityExplicitDirection
+      case data: Aggregate =>
+        data.specifiedDirection match {
+          // Recurse into children to ensure explicit direction set somewhere
+          case SpecifiedDirection.Unspecified | SpecifiedDirection.Flip =>
+            data match {
+              case record: Record =>
+                record.elementsIterator.foreach(assignCompatDir(_))
+              case vec: Vec[_] =>
+                vec.elementsIterator.foreach(assignCompatDir(_))
+                assignCompatDir(vec.sample_element) // This is used in fromChildren computation
+            }
+          case SpecifiedDirection.Input | SpecifiedDirection.Output =>
+          // forced assign, nothing to do
+          // The .bind algorithm will automatically assign the direction here.
+          // Thus, no implicit assignment is necessary.
+        }
+    }
+  }
 }
 
 /** Abstract base class for Modules, which behave much like Verilog modules.
@@ -382,6 +414,10 @@ package internal {
           new ClonePorts(proto.getChiselPorts :+ ("io" -> b._io.get): _*)
         case _ => new ClonePorts(proto.getChiselPorts: _*)
       }
+      // getChiselPorts (nor cloneTypeFull in general)
+      // does not recursively copy the right specifiedDirection,
+      // still need to fix it up here.
+      Module.assignCompatDir(clonePorts)
       clonePorts.bind(PortBinding(cloneParent))
       clonePorts.setAllParents(Some(cloneParent))
       cloneParent._portsRecord = clonePorts
@@ -691,35 +727,8 @@ package experimental {
       * io, then do operations on it. This binds a Chisel type in-place (mutably) as an IO.
       */
     protected def _bindIoInPlace(iodef: Data): Unit = {
-      // Compatibility code: Chisel2 did not require explicit direction on nodes
-      //   (unspecified treated as output, and flip on nothing was input).
-      // However, we are going to go back to Chisel2 semantics, so we need to make it work
-      //   even for chisel3 code.
-      // This assigns the explicit directions required by both semantics on all Bundles.
-      // This recursively walks the tree, and assigns directions if no explicit
-      //   direction given by upper-levels (override Input / Output)
-      def assignCompatDir(data: Data): Unit = {
-        data match {
-          case data: Element => data._assignCompatibilityExplicitDirection
-          case data: Aggregate =>
-            data.specifiedDirection match {
-              // Recurse into children to ensure explicit direction set somewhere
-              case SpecifiedDirection.Unspecified | SpecifiedDirection.Flip =>
-                data match {
-                  case record: Record =>
-                    record.elementsIterator.foreach(assignCompatDir(_))
-                  case vec: Vec[_] =>
-                    vec.elementsIterator.foreach(assignCompatDir(_))
-                }
-              case SpecifiedDirection.Input | SpecifiedDirection.Output =>
-              // forced assign, nothing to do
-              // Note this is because Input and Output recurse down their types to align all fields to that SpecifiedDirection
-              // Thus, no implicit assigment is necessary.
-            }
-        }
-      }
-
-      assignCompatDir(iodef)
+      // Assign any signals (Chisel or chisel3) with Unspecified/Flipped directions to Output/Input
+      Module.assignCompatDir(iodef)
 
       iodef.bind(PortBinding(this))
       _ports += iodef
diff --git a/src/test/scala/chiselTests/CompatibilityInteroperabilitySpec.scala b/src/test/scala/chiselTests/CompatibilityInteroperabilitySpec.scala
index e2fb2179bee..eb5aaabab1a 100644
--- a/src/test/scala/chiselTests/CompatibilityInteroperabilitySpec.scala
+++ b/src/test/scala/chiselTests/CompatibilityInteroperabilitySpec.scala
@@ -392,6 +392,290 @@ class CompatibilityInteroperabilitySpec extends ChiselFlatSpec {
     compile(new Top(false))
   }
 
+  "A Chisel.Bundle with only unspecified directions" should "work with D/I" in {
+
+    object Compat {
+      import Chisel._
+      import chisel3.experimental.hierarchy.{instantiable, public}
+
+      class CompatBiDirUnspecifiedBundle extends Bundle {
+        val out = Bool()
+        val in = Flipped(Bool())
+      }
+
+      @instantiable
+      class CompatModule extends Module {
+        @public val io = IO(new CompatBiDirUnspecifiedBundle)
+      }
+    }
+
+    object Chisel3 {
+      import chisel3._
+      import chisel3.experimental.hierarchy.Instance
+      class Example extends Module {
+        val mod = Module(new Compat.CompatModule())
+        mod.io.in <> DontCare
+        val inst = Instance(mod.toDefinition)
+        inst.io.in <> mod.io.out
+        mod.io.in <> inst.io.out
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A Chisel.Bundle with mixed Specified and Unspecified directions" should "work with D/I" in {
+
+    object Compat {
+      import Chisel._
+      import chisel3.experimental.hierarchy.{instantiable, public}
+
+      class CompatBiDirMixedBundle extends Bundle {
+        val out = Bool()
+        val in = Flipped(Bool())
+        val explicit = Output(Bool())
+      }
+
+      @instantiable
+      class CompatModule extends Module {
+        @public val io = IO(new CompatBiDirMixedBundle)
+      }
+    }
+
+    object Chisel3 {
+      import chisel3._
+      import chisel3.experimental.hierarchy.Instance
+      class Example extends Module {
+        val mod = Module(new Compat.CompatModule)
+        mod.io.in <> DontCare
+        val inst = Instance(mod.toDefinition)
+        inst.io.in <> mod.io.out
+        mod.io.in <> inst.io.out
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A Chisel.Bundle with only unspecified vec direction" should "work with D/I" in {
+
+    object Compat {
+      import Chisel._
+      import chisel3.experimental.hierarchy.{instantiable, public}
+
+      class CompatBiDirUnspecifiedVecBundle extends Bundle {
+        val out = Vec(3, Bool())
+        val in = Flipped(Vec(3, Bool()))
+      }
+
+      @instantiable
+      class CompatModule extends Module {
+        @public val io = IO(new CompatBiDirUnspecifiedVecBundle)
+      }
+    }
+
+    object Chisel3 {
+      import chisel3._
+      import chisel3.experimental.hierarchy.Instance
+      class Example extends Module {
+        val mod = Module(new Compat.CompatModule())
+        mod.io.in <> DontCare
+        val inst = Instance(mod.toDefinition)
+        inst.io.in <> mod.io.out
+        mod.io.in <> inst.io.out
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A chisel3.Bundle with only unspecified directions" should "work with D/I" in {
+
+    // This test is NOT expected to work on 3.5.x, it should throw an error in the IO construction.
+
+    object Chisel3 {
+      import chisel3._
+      import chisel3.experimental.hierarchy.{instantiable, public, Instance}
+
+      class BiDirUnspecifiedBundle extends Bundle {
+        val out = Bool()
+        val in = Flipped(Bool())
+      }
+
+      @instantiable
+      class MyModule extends Module {
+        @public val io = IO(new BiDirUnspecifiedBundle)
+        io <> DontCare
+      }
+
+      class Example extends Module {
+        val mod = Module(new MyModule())
+        mod.io.in <> DontCare
+        val inst = Instance(mod.toDefinition)
+        inst.io.in <> mod.io.out
+        mod.io.in <> inst.io.out
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A chisel3.Bundle with mixed Specified and Unspecified directions" should "work with D/I" in {
+
+    // This test is NOT expected to work on 3.5.x, it should throw an error in the IO construction.
+
+    object Chisel3 {
+      import chisel3._
+      import chisel3.experimental.hierarchy.{instantiable, public, Instance}
+
+      class BiDirMixedBundle extends Bundle {
+        val out = Bool()
+        val in = Flipped(Bool())
+        val explicit = Output(Bool())
+      }
+
+      @instantiable
+      class MyModule extends Module {
+        @public val io = IO(new BiDirMixedBundle)
+        io <> DontCare
+      }
+      class Example extends Module {
+        val mod = Module(new MyModule)
+        mod.io.in <> DontCare
+        val inst = Instance(mod.toDefinition)
+        inst.io.in <> mod.io.out
+        mod.io.in <> inst.io.out
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A chisel3.Bundle with only unspecified vec direction" should "work with D/I" in {
+
+    // This test is NOT expected to work on 3.5.x, it should throw an error in the IO construction
+
+    object Chisel3 {
+      import chisel3._
+      import chisel3.experimental.hierarchy.{instantiable, public, Instance}
+
+      class BiDirUnspecifiedVecBundle extends Bundle {
+        val out = Vec(3, Bool())
+        val in = Flipped(Vec(3, Bool()))
+      }
+
+      @instantiable
+      class MyModule extends Module {
+        @public val io = IO(new BiDirUnspecifiedVecBundle)
+        io <> DontCare
+      }
+
+      class Example extends Module {
+        val mod = Module(new MyModule())
+        mod.io.in <> DontCare
+        val inst = Instance(mod.toDefinition)
+        inst.io.in <> mod.io.out
+        mod.io.in <> inst.io.out
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A chisel3.Bundle with only unspecified vec direction within an unspecified direction parent Bundle" should "work with D/I" in {
+
+    // This test is NOT expected to work in 3.5.x, it should throw an error in the IO construction.
+
+    object Chisel3 {
+      import chisel3._
+      import chisel3.experimental.hierarchy.{instantiable, public, Instance}
+
+      class UnspecifiedVecBundle extends Bundle {
+        val vec = Vec(3, Bool())
+      }
+
+      class UnspecifiedParentBundle extends Bundle {
+        val out = new UnspecifiedVecBundle
+      }
+
+      @instantiable
+      class MyModule extends Module {
+        @public val io = IO(new UnspecifiedParentBundle)
+        io <> DontCare
+      }
+
+      class Example extends Module {
+        val mod = Module(new MyModule())
+
+        val wire = Wire(new UnspecifiedParentBundle)
+        wire.out.vec <> mod.io.out.vec
+        val inst = Instance(mod.toDefinition)
+        wire.out.vec <> inst.io.out.vec
+
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A undirectioned Chisel.Bundle used in a MixedVec " should "bulk connect in import chisel3._ code correctly" in {
+
+    // This test is NOT expected to work on 3.5.x, it should throw an error in the IO construction.
+
+    object Compat {
+
+      import Chisel._
+      import chisel3.util.MixedVec
+
+      class ChiselModule extends Module {
+        val io = IO(new Bundle {
+          val out = MixedVec(Seq.fill(3) { Bool() })
+          val in = Flipped(MixedVec(Seq.fill(3) { Bool() }))
+        })
+        io.out := RegNext(io.in)
+      }
+
+    }
+    object Chisel3 {
+      import chisel3._
+
+      class Chisel3Module extends Compat.ChiselModule
+
+      class Example extends Module {
+        val oldMod = Module(new Compat.ChiselModule)
+        val newMod = Module(new Chisel3Module)
+
+        oldMod.io.in <> DontCare
+        newMod.io.in <> DontCare
+
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
+  "A undirectioned Chisel.Bundle with Records with undirectioned and directioned fields " should "work" in {
+
+    // This test should fail on 3.5.x
+
+    object Compat {
+
+      import Chisel._
+
+      class ChiselModule(gen: () => Data) extends Module {
+        val io = IO(new Bundle {
+          val mixed = new Chisel3.MyRecord(gen)
+        })
+      }
+
+    }
+    object Chisel3 {
+      import chisel3._
+      import scala.collection.immutable.SeqMap
+
+      class MyRecord(gen: () => Data) extends Record with chisel3.experimental.AutoCloneType {
+        val elements = SeqMap("genDirectioned" -> Output(gen()), "genUndirectioned" -> gen())
+      }
+
+      class Example extends Module {
+        val newMod = Module(new Compat.ChiselModule(() => Bool()))
+      }
+    }
+    compile(new Chisel3.Example)
+  }
+
   "A BlackBox with Chisel._ fields in its IO" should "bulk connect in import chisel3._ code correctly" in {
     object Compat {
       import Chisel._