diff --git a/lib/IRGen/GenClass.cpp b/lib/IRGen/GenClass.cpp
index 31fe80a118ad3..53b2afac7e026 100644
--- a/lib/IRGen/GenClass.cpp
+++ b/lib/IRGen/GenClass.cpp
@@ -16,6 +16,9 @@
 
 #include "GenClass.h"
 
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/RecordLayout.h"
 #include "swift/ABI/Class.h"
 #include "swift/ABI/MetadataValues.h"
 #include "swift/AST/ASTContext.h"
@@ -28,6 +31,7 @@
 #include "swift/AST/SemanticAttrs.h"
 #include "swift/AST/TypeMemberVisitor.h"
 #include "swift/AST/Types.h"
+#include "swift/Basic/Defer.h"
 #include "swift/ClangImporter/ClangModule.h"
 #include "swift/IRGen/Linking.h"
 #include "swift/SIL/SILModule.h"
@@ -281,6 +285,55 @@ namespace {
                                superclass);
     }
 
+    void maybeAddCxxRecordBases(ClassDecl *cd) {
+      auto cxxRecord = dyn_cast_or_null<clang::CXXRecordDecl>(cd->getClangDecl());
+      if (!cxxRecord)
+        return;
+
+      auto &layout = cxxRecord->getASTContext().getASTRecordLayout(cxxRecord);
+
+      for (auto base : cxxRecord->bases()) {
+        if (base.isVirtual())
+          continue;
+
+        auto baseType = base.getType().getCanonicalType();
+
+        auto baseRecord = cast<clang::RecordType>(baseType)->getDecl();
+        auto baseCxxRecord = cast<clang::CXXRecordDecl>(baseRecord);
+
+        if (baseCxxRecord->isEmpty())
+          continue;
+
+        auto offset = Size(layout.getBaseClassOffset(baseCxxRecord).getQuantity());
+        auto size = Size(cxxRecord->getASTContext().getTypeSizeInChars(baseType).getQuantity());
+
+        if (offset != CurSize) {
+          assert(offset > CurSize);
+          auto paddingSize = offset - CurSize;
+          auto &opaqueTI = IGM.getOpaqueStorageTypeInfo(paddingSize, Alignment(1));
+          auto element = ElementLayout::getIncomplete(opaqueTI);
+          addField(element, LayoutStrategy::Universal);
+        }
+
+        auto &opaqueTI = IGM.getOpaqueStorageTypeInfo(size, Alignment(1));
+        auto element = ElementLayout::getIncomplete(opaqueTI);
+        addField(element, LayoutStrategy::Universal);
+      }
+    }
+
+    void addPaddingBeforeClangField(const clang::FieldDecl *fd) {
+      auto offset = Size(fd->getASTContext().toCharUnitsFromBits(
+          fd->getASTContext().getFieldOffset(fd)).getQuantity());
+
+      if (offset != CurSize) {
+        assert(offset > CurSize);
+        auto paddingSize = offset - CurSize;
+        auto &opaqueTI = IGM.getOpaqueStorageTypeInfo(paddingSize, Alignment(1));
+        auto element = ElementLayout::getIncomplete(opaqueTI);
+        addField(element, LayoutStrategy::Universal);
+      }
+    }
+
     void addDirectFieldsFromClass(ClassDecl *rootClass, SILType rootClassType,
                                   ClassDecl *theClass, SILType classType,
                                   bool superclass) {
@@ -290,7 +343,9 @@ namespace {
                                                ->getRecursiveProperties()
                                                .hasUnboundGeneric());
 
-      forEachField(IGM, theClass, [&](Field field) {
+      maybeAddCxxRecordBases(theClass);
+
+      auto fn = [&](Field field) {
         // Ignore missing properties here; we should have flagged these
         // with the classHasIncompleteLayout call above.
         if (!field.isConcrete()) {
@@ -325,7 +380,25 @@ namespace {
           AllStoredProperties.push_back(field);
           AllFieldAccesses.push_back(getFieldAccess(isKnownEmpty));
         }
-      });
+      };
+
+      auto classDecl = dyn_cast<ClassDecl>(theClass);
+      if (classDecl && classDecl->isRootDefaultActor()) {
+        fn(Field::DefaultActorStorage);
+      }
+
+      for (auto decl :
+           theClass->getStoredPropertiesAndMissingMemberPlaceholders()) {
+        if (decl->getClangDecl())
+          if (auto clangField = cast<clang::FieldDecl>(decl->getClangDecl()))
+            addPaddingBeforeClangField(clangField);
+
+        if (auto var = dyn_cast<VarDecl>(decl)) {
+          fn(var);
+        } else {
+          fn(cast<MissingMemberDecl>(decl));
+        }
+      }
 
       if (!superclass) {
         // If we're calculating the layout of a specialized generic class type,
diff --git a/test/Interop/Cxx/foreign-reference/Inputs/member-layout.h b/test/Interop/Cxx/foreign-reference/Inputs/member-layout.h
new file mode 100644
index 0000000000000..a655ac54ebd87
--- /dev/null
+++ b/test/Interop/Cxx/foreign-reference/Inputs/member-layout.h
@@ -0,0 +1,56 @@
+#ifndef TEST_INTEROP_CXX_FOREIGN_REFERENCE_INPUTS_NULLABLE_H
+#define TEST_INTEROP_CXX_FOREIGN_REFERENCE_INPUTS_NULLABLE_H
+
+struct IntHolder { int value; };
+
+struct
+    __attribute__((swift_attr("import_reference")))
+    __attribute__((swift_attr("retain:immortal")))
+    __attribute__((swift_attr("release:immortal")))
+    IntBase : IntHolder {
+  int i;
+};
+
+struct NoDtorThreeByte {
+  char x;
+  char y;
+  char z;
+  ~NoDtorThreeByte() = delete;
+};
+
+struct
+    __attribute__((swift_attr("import_reference")))
+    __attribute__((swift_attr("retain:immortal")))
+    __attribute__((swift_attr("release:immortal")))
+    IntCharRef {
+  int i;
+  char b;
+};
+
+struct
+    __attribute__((swift_attr("import_reference")))
+    __attribute__((swift_attr("retain:immortal")))
+    __attribute__((swift_attr("release:immortal")))
+    IntCharValue {
+  int i;
+  char b;
+};
+
+
+struct
+    __attribute__((swift_attr("import_reference")))
+    __attribute__((swift_attr("retain:immortal")))
+    __attribute__((swift_attr("release:immortal")))
+    UnimportableMemberRef {
+  int z; int zz; NoDtorThreeByte x; NoDtorThreeByte xx; int y;
+};
+
+struct
+    __attribute__((swift_attr("import_reference")))
+    __attribute__((swift_attr("retain:immortal")))
+    __attribute__((swift_attr("release:immortal")))
+    UnimportableMemberValue {
+  int z; int zz; NoDtorThreeByte x; NoDtorThreeByte xx; int y;
+};
+
+#endif // TEST_INTEROP_CXX_FOREIGN_REFERENCE_INPUTS_NULLABLE_H
diff --git a/test/Interop/Cxx/foreign-reference/Inputs/module.modulemap b/test/Interop/Cxx/foreign-reference/Inputs/module.modulemap
index 173238cf21711..159b2b182094a 100644
--- a/test/Interop/Cxx/foreign-reference/Inputs/module.modulemap
+++ b/test/Interop/Cxx/foreign-reference/Inputs/module.modulemap
@@ -27,3 +27,8 @@ module ReferenceCounted {
   header "reference-counted.h"
   requires cplusplus
 }
+
+module MemberLayout {
+  header "member-layout.h"
+  requires cplusplus
+}
diff --git a/test/Interop/Cxx/foreign-reference/base-class-layout-irgen.swift b/test/Interop/Cxx/foreign-reference/base-class-layout-irgen.swift
new file mode 100644
index 0000000000000..6038052a5f590
--- /dev/null
+++ b/test/Interop/Cxx/foreign-reference/base-class-layout-irgen.swift
@@ -0,0 +1,13 @@
+// RUN: %target-swift-emit-ir %s -I %S/Inputs -enable-experimental-cxx-interop -module-name=test  | %FileCheck %s
+//
+// XFAIL: OS=linux-android, OS=linux-androideabi
+
+import MemberLayout
+
+// CHECK: %TSo7IntBaseV = type <{ [4 x i8], %Ts5Int32V }>
+
+// CHECK-LABEL: define {{.*}}swiftcc i32 @"$s4testAA1ys5Int32VSo7IntBaseV_tF"(%TSo7IntBaseV* %0)
+// CHECK: getelementptr inbounds %TSo7IntBaseV, %TSo7IntBaseV* %0, i32 0, i32 1
+public func test(y: IntBase) -> CInt {
+  return y.i
+}
diff --git a/test/Interop/Cxx/foreign-reference/unimportable-member-layout-irgen.swift b/test/Interop/Cxx/foreign-reference/unimportable-member-layout-irgen.swift
new file mode 100644
index 0000000000000..54ac0b27df418
--- /dev/null
+++ b/test/Interop/Cxx/foreign-reference/unimportable-member-layout-irgen.swift
@@ -0,0 +1,38 @@
+// RUN: %target-swift-emit-ir %s -I %S/Inputs -enable-experimental-cxx-interop -module-name=test | %FileCheck %s
+//
+// XFAIL: OS=linux-android, OS=linux-androideabi
+
+import MemberLayout
+
+// Make sure the "refs" and "values" look *exactly* the same.
+
+// CHECK: %TSo10IntCharRefV = type <{ %Ts5Int32V, %Ts4Int8V }>
+// CHECK: %TSo12IntCharValueV = type <{ %Ts5Int32V, %Ts4Int8V }>
+
+// CHECK: %TSo21UnimportableMemberRefV = type <{ %Ts5Int32V, %Ts5Int32V, [8 x i8], %Ts5Int32V }>
+// CHECK: %TSo23UnimportableMemberValueV = type <{ %Ts5Int32V, %Ts5Int32V, [8 x i8], %Ts5Int32V }>
+
+// CHECK-LABEL: define {{.*}}swiftcc i8 @"$s4testAA1ys4Int8VSo10IntCharRefV_tF"(%TSo10IntCharRefV* %0)
+// CHECK: getelementptr inbounds %TSo10IntCharRefV, %TSo10IntCharRefV* %0, i32 0, i32 1
+public func test(y: IntCharRef) -> CChar {
+  return y.b
+}
+
+// CHECK-LABEL: define {{.*}}swiftcc i8 @"$s4testAA1ys4Int8VSo12IntCharValueV_tF"(%TSo12IntCharValueV* %0)
+// CHECK: getelementptr inbounds %TSo12IntCharValueV, %TSo12IntCharValueV* %0, i32 0, i32 1
+public func test(y: IntCharValue) -> CChar {
+  return y.b
+}
+
+// CHECK-LABEL: define {{.*}}swiftcc i32 @"$s4testAA1ys5Int32VSo21UnimportableMemberRefV_tF"(%TSo21UnimportableMemberRefV* %0)
+// CHECK: getelementptr inbounds %TSo21UnimportableMemberRefV, %TSo21UnimportableMemberRefV* %0, i32 0, i32 3
+public func test(y: UnimportableMemberRef) -> CInt {
+  return y.y
+}
+
+// CHECK-LABEL: define {{.*}}swiftcc i32 @"$s4testAA1ys5Int32VSo23UnimportableMemberValueV_tF"(%TSo23UnimportableMemberValueV* %0)
+// CHECK: getelementptr inbounds %TSo23UnimportableMemberValueV, %TSo23UnimportableMemberValueV* %0, i32 0, i32 3
+public func test(y: UnimportableMemberValue) -> CInt {
+  return y.y
+}
+