diff --git a/lib/Serialization/Deserialization.cpp b/lib/Serialization/Deserialization.cpp
index 03244b0acc5..6a12d8902fb 100644
--- a/lib/Serialization/Deserialization.cpp
+++ b/lib/Serialization/Deserialization.cpp
@@ -944,15 +944,15 @@ Decl *ModuleFile::getDecl(DeclID DID, Optional<DeclContext *> ForcedContext,
 
   case decls_block::CONSTRUCTOR_DECL: {
     DeclID parentID;
-    bool isImplicit, hasSelectorStyleSignature, isObjC;
+    bool isImplicit, hasSelectorStyleSignature, isObjC, isTransparent;
     TypeID signatureID;
     TypeID interfaceID;
     DeclID implicitSelfID;
 
     decls_block::ConstructorLayout::readRecord(scratch, parentID, isImplicit,
                                                hasSelectorStyleSignature,
-                                               isObjC, signatureID,
-                                               interfaceID,
+                                               isObjC, isTransparent,
+                                               signatureID, interfaceID,
                                                implicitSelfID);
     auto parent = getDeclContext(parentID);
     if (declOrOffset.isComplete())
@@ -1026,6 +1026,8 @@ Decl *ModuleFile::getDecl(DeclID DID, Optional<DeclContext *> ForcedContext,
     if (hasSelectorStyleSignature)
       ctor->setHasSelectorStyleSignature();
     ctor->setIsObjC(isObjC);
+    if (isTransparent)
+      ctor->getMutableAttrs().setAttr(AK_transparent, SourceLoc());
 
     if (genericParams)
       for (auto &genericParam : *ctor->getGenericParams())
diff --git a/lib/Serialization/ModuleFormat.h b/lib/Serialization/ModuleFormat.h
index f12076dc3e0..ebaafe0e0d6 100644
--- a/lib/Serialization/ModuleFormat.h
+++ b/lib/Serialization/ModuleFormat.h
@@ -625,6 +625,7 @@ namespace decls_block {
     BCFixed<1>,  // implicit?
     BCFixed<1>,  // has selector-style signature?
     BCFixed<1>,  // objc?
+    BCFixed<1>,  // transparent?
     TypeIDField, // type (signature)
     TypeIDField, // type (interface)
     DeclIDField  // implicit this decl
@@ -654,7 +655,7 @@ namespace decls_block {
     BCFixed<1>,   // class method?
     BCFixed<1>,   // assignment? / conversion?
     BCFixed<1>,   // explicitly objc?
-    BCFixed<1>,   // iboutlet?
+    BCFixed<1>,   // ibaction?
     BCFixed<1>,   // transparent?
     BCVBR<5>,     // number of parameter patterns
     TypeIDField,  // type (signature)
diff --git a/lib/Serialization/Serialization.cpp b/lib/Serialization/Serialization.cpp
index ad131aa0c3a..427d172e2e8 100644
--- a/lib/Serialization/Serialization.cpp
+++ b/lib/Serialization/Serialization.cpp
@@ -943,6 +943,12 @@ void Serializer::writeDecl(const Decl *D) {
   case DeclKind::Extension: {
     auto extension = cast<ExtensionDecl>(D);
 
+    DeclAttributes remainingAttrs = extension->getAttrs();
+    // @transparent on extensions is propagated down to the methods and
+    // constructors during serialization.
+    remainingAttrs.clearAttribute(AK_transparent);
+    assert(remainingAttrs.empty() && "unhandled extension attrs");
+
     const Decl *DC = getDeclForContext(extension->getDeclContext());
     Type baseTy = extension->getExtendedType();
 
@@ -1260,7 +1266,7 @@ void Serializer::writeDecl(const Decl *D) {
                              fn->getAttrs().isConversion(),
                            fn->isObjC(),
                            fn->getAttrs().isIBAction(),
-                           fn->getAttrs().isTransparent(),
+                           fn->isTransparent(),
                            fn->getArgParamPatterns().size(),
                            addTypeRef(fn->getType()),
                            addTypeRef(fn->getInterfaceType()),
@@ -1345,6 +1351,7 @@ void Serializer::writeDecl(const Decl *D) {
                                   ctor->isImplicit(),
                                   ctor->hasSelectorStyleSignature(),
                                   ctor->isObjC(),
+                                  ctor->isTransparent(),
                                   addTypeRef(ctor->getType()),
                                   addTypeRef(ctor->getInterfaceType()),
                                   addDeclRef(implicitSelf));