diff --git a/include/swift/Serialization/ModuleFormat.h b/include/swift/Serialization/ModuleFormat.h
index 58eea077167..bace12dfc26 100644
--- a/include/swift/Serialization/ModuleFormat.h
+++ b/include/swift/Serialization/ModuleFormat.h
@@ -52,7 +52,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 465; // Last change: Remove owning addressors
+const uint16_t SWIFTMODULE_VERSION_MINOR = 466; // Last change: add isAutoClosure flag to param
 
 using DeclIDField = BCFixed<31>;
 
@@ -1024,6 +1024,7 @@ namespace decls_block {
     VarDeclSpecifierField, // specifier
     TypeIDField,           // interface type
     BCFixed<1>,            // isVariadic?
+    BCFixed<1>,            // isAutoClosure?
     DefaultArgumentField,  // default argument kind
     BCBlob                 // default argument text
   >;
diff --git a/lib/Serialization/Deserialization.cpp b/lib/Serialization/Deserialization.cpp
index cbe325c8742..9f220db4e0e 100644
--- a/lib/Serialization/Deserialization.cpp
+++ b/lib/Serialization/Deserialization.cpp
@@ -3029,12 +3029,13 @@ ModuleFile::getDeclCheckedImpl(DeclID DID) {
     unsigned rawSpecifier;
     TypeID interfaceTypeID;
     bool isVariadic;
+    bool isAutoClosure;
     uint8_t rawDefaultArg;
 
     decls_block::ParamLayout::readRecord(scratch, argNameID, paramNameID,
                                          contextID, rawSpecifier,
                                          interfaceTypeID, isVariadic,
-                                         rawDefaultArg);
+                                         isAutoClosure, rawDefaultArg);
 
     auto DC = getDeclContext(contextID);
     if (declOrOffset.isComplete())
@@ -3065,6 +3066,7 @@ ModuleFile::getDeclCheckedImpl(DeclID DID) {
 
     param->setInterfaceType(paramTy);
     param->setVariadic(isVariadic);
+    param->setAutoClosure(isAutoClosure);
 
     // Decode the default argument kind.
     // FIXME: Default argument expression, if available.
diff --git a/lib/Serialization/Serialization.cpp b/lib/Serialization/Serialization.cpp
index 6e88131c473..c1d4ee4dd4e 100644
--- a/lib/Serialization/Serialization.cpp
+++ b/lib/Serialization/Serialization.cpp
@@ -3228,6 +3228,7 @@ void Serializer::writeDecl(const Decl *D) {
         getRawStableVarDeclSpecifier(param->getSpecifier()),
         addTypeRef(interfaceType),
         param->isVariadic(),
+        param->isAutoClosure(),
         getRawStableDefaultArgumentKind(param->getDefaultArgumentKind()),
         defaultArgumentText);