diff --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
--- a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -765,8 +765,8 @@
   // context header.
   case coro::ABI::Async: {
     auto *ActiveAsyncSuspend = cast<CoroSuspendAsyncInst>(ActiveSuspend);
-    auto *CalleeContext =
-        NewF->getArg(ActiveAsyncSuspend->getStorageArgumentIndex());
+    auto ContextIdx = ActiveAsyncSuspend->getStorageArgumentIndex() & 0xff;
+    auto *CalleeContext = NewF->getArg(ContextIdx);
     auto *FramePtrTy = Shape.FrameTy->getPointerTo();
     auto *ProjectionFunc =
         ActiveAsyncSuspend->getAsyncContextProjectionFunction();
@@ -827,6 +827,13 @@
   Attrs = Attrs.addParamAttributes(Context, ParamIndex, ParamAttrs);
 }
 
+static void addSwiftSelfAttrs(AttributeList &Attrs, LLVMContext &Context,
+                              unsigned ParamIndex) {
+  AttrBuilder ParamAttrs;
+  ParamAttrs.addAttribute(Attribute::SwiftSelf);
+  Attrs = Attrs.addParamAttributes(Context, ParamIndex, ParamAttrs);
+}
+
 /// Clone the body of the original function into a resume function of
 /// some sort.
 void CoroCloner::create() {
@@ -949,8 +956,16 @@
     auto *ActiveAsyncSuspend = cast<CoroSuspendAsyncInst>(ActiveSuspend);
     if (OrigF.hasParamAttribute(Shape.AsyncLowering.ContextArgNo,
                                 Attribute::SwiftAsync)) {
-      auto ContextArgIndex = ActiveAsyncSuspend->getStorageArgumentIndex();
+      uint32_t ArgAttributeIndices =
+          ActiveAsyncSuspend->getStorageArgumentIndex();
+      auto ContextArgIndex = ArgAttributeIndices & 0xff;
       addAsyncContextAttrs(NewAttrs, Context, ContextArgIndex);
+
+      // `swiftasync` must preceed `swiftself` so 0 is not a valid index for
+      // `swiftself`.
+      auto SwiftSelfIndex = ArgAttributeIndices >> 8;
+      if (SwiftSelfIndex)
+        addSwiftSelfAttrs(NewAttrs, Context, SwiftSelfIndex);
     }
     break;
   }
diff --git a/llvm/test/Transforms/Coroutines/coro-async.ll b/llvm/test/Transforms/Coroutines/coro-async.ll
--- a/llvm/test/Transforms/Coroutines/coro-async.ll
+++ b/llvm/test/Transforms/Coroutines/coro-async.ll
@@ -410,7 +410,7 @@
      i32 64    ; Initial async context size without space for frame
 }>
 
-define swiftcc void @polymorphic_suspend_return(i8* %async.ctxt, %async.task* %task, %async.actor* %actor)  {
+define swiftcc void @polymorphic_suspend_return(i8* swiftasync %async.ctxt, %async.task* %task, %async.actor* %actor)  {
 entry:
   %tmp = alloca { i64, i64 }, align 8
   %proj.1 = getelementptr inbounds { i64, i64 }, { i64, i64 }* %tmp, i64 0, i32 0
@@ -445,7 +445,7 @@
   %resume_proj_fun = bitcast i8*(i8*)* @resume_context_projection to i8*
   %callee = bitcast void(i8*, %async.task*, %async.actor*)* @asyncSuspend to i8*
   %res = call {i8*, i8*, i8*, i8*} (i32, i8*, i8*, ...)
-         @llvm.coro.suspend.async.sl_p0i8p0i8p0i8p0i8s(i32 0,
+         @llvm.coro.suspend.async.sl_p0i8p0i8p0i8p0i8s(i32 256, ;; swiftasync at 0 and swiftself at 1 in resume function
                                                  i8* %resume.func_ptr,
                                                  i8* %resume_proj_fun,
                                                  void (i8*, i8*, %async.task*, %async.actor*)* @my_async_function.my_other_async_function_fp.apply,
@@ -464,8 +464,8 @@
   unreachable
 }
 
-; CHECK-LABEL: define swiftcc void @polymorphic_suspend_return(i8* %async.ctxt, %async.task* %task, %async.actor* %actor)
-; CHECK-LABEL: define internal swiftcc void @polymorphic_suspend_return.resume.0(i8* {{.*}}%0, i8* {{.*}}%1, i8* {{.*}}%2, i8* {{.*}}%3)
+; CHECK-LABEL: define swiftcc void @polymorphic_suspend_return(i8* swiftasync %async.ctxt, %async.task* %task, %async.actor* %actor)
+; CHECK-LABEL: define internal swiftcc void @polymorphic_suspend_return.resume.0(i8* {{.*}}swiftasync{{.*}} %0, i8* {{.*}}swiftself{{.*}} %1, i8* {{.*}}%2, i8* {{.*}}%3)
 ; CHECK: bitcast i8* %3 to %async.task*
 ; CHECK: }