diff --git a/lib/SILGen/SILGenBackDeploy.cpp b/lib/SILGen/SILGenBackDeploy.cpp
index 261539f1f0fed..c6e767604cf60 100644
--- a/lib/SILGen/SILGenBackDeploy.cpp
+++ b/lib/SILGen/SILGenBackDeploy.cpp
@@ -178,20 +178,28 @@ void SILGenFunction::emitBackDeploymentThunk(SILDeclRef thunk) {
 
   F.setGenericEnvironment(SGM.Types.getConstantGenericEnvironment(thunk));
 
-  emitBasicProlog(FD->getParameters(), FD->getImplicitSelfDecl(),
-                  FD->getResultInterfaceType(), FD, FD->hasThrows(),
-                  FD->getThrowsLoc());
-  prepareEpilog(FD->getResultInterfaceType(), FD->hasThrows(),
-                CleanupLocation(FD));
+  // Generate the thunk prolog by collecting parameters.
+  SmallVector<ManagedValue, 4> params;
+  SmallVector<SILArgument *, 4> indirectParams;
+  collectThunkParams(loc, params, &indirectParams);
 
-  // Gather the entry block's arguments up so that we can forward them.
+  // Build up the list of arguments that we're going to invoke the the real
+  // function with.
   SmallVector<SILValue, 8> paramsForForwarding;
-  SILBasicBlock *entryBlock = getFunction().getEntryBlock();
-  for (SILArgument *arg :
-       make_range(entryBlock->args_begin(), entryBlock->args_end())) {
-    paramsForForwarding.emplace_back(arg);
+  for (auto indirectParam : indirectParams) {
+    paramsForForwarding.emplace_back(indirectParam);
+  }
+
+  for (auto param : params) {
+    // We're going to directly call either the original function or the fallback
+    // function with these arguments and then return. Therefore we just forward
+    // the arguments instead of handling their ownership conventions.
+    paramsForForwarding.emplace_back(param.forward(*this));
   }
 
+  prepareEpilog(FD->getResultInterfaceType(), FD->hasThrows(),
+                CleanupLocation(FD));
+
   SILBasicBlock *availableBB = createBasicBlock("availableBB");
   SILBasicBlock *unavailableBB = createBasicBlock("unavailableBB");
 
diff --git a/test/SILGen/back_deploy_attribute_generic_func.swift b/test/SILGen/back_deploy_attribute_generic_func.swift
index 3cfb303eaaae2..5831d85215ec2 100644
--- a/test/SILGen/back_deploy_attribute_generic_func.swift
+++ b/test/SILGen/back_deploy_attribute_generic_func.swift
@@ -5,14 +5,14 @@
 
 // REQUIRES: OS=macosx
 
-// -- Fallback definition of genericFunc()
+// -- Fallback definition of genericFunc(_:)
 // CHECK-LABEL: sil non_abi [serialized] [ossa] @$s11back_deploy11genericFuncyxxlFTwB : $@convention(thin) <T> (@in_guaranteed T) -> @out T
 // CHECK: bb0([[OUT_ARG:%.*]] : $*T, [[IN_ARG:%.*]] : $*T):
 // CHECK:   copy_addr [[IN_ARG]] to [init] [[OUT_ARG]] : $*T
 // CHECK:   [[RESULT:%.*]] = tuple ()
 // CHECK:   return [[RESULT]] : $()
 
-// -- Back deployment thunk for genericFunc()
+// -- Back deployment thunk for genericFunc(_:)
 // CHECK-LABEL: sil non_abi [serialized] [thunk] [ossa] @$s11back_deploy11genericFuncyxxlFTwb : $@convention(thin) <T> (@in_guaranteed T) -> @out T
 // CHECK: bb0([[OUT_ARG:%.*]] : $*T, [[IN_ARG:%.*]] : $*T):
 // CHECK:   [[MAJOR:%.*]] = integer_literal $Builtin.Word, 10
@@ -36,16 +36,58 @@
 // CHECK:   [[RESULT:%.*]] = tuple ()
 // CHECK:   return [[RESULT]] : $()
 
-// -- Original definition of genericFunc()
+// -- Original definition of genericFunc(_:)
 // CHECK-LABEL: sil [available 10.52] [ossa] @$s11back_deploy11genericFuncyxxlF : $@convention(thin) <T> (@in_guaranteed T) -> @out T
 @_backDeploy(before: macOS 10.52)
 public func genericFunc<T>(_ t: T) -> T {
   return t
 }
 
+// -- Fallback definition of genericFuncWithOwnedParam(_:)
+// CHECK-LABEL: sil non_abi [serialized] [ossa] @$s11back_deploy25genericFuncWithOwnedParamyyxnlFTwB : $@convention(thin) <T> (@in T) -> ()
+// CHECK: bb0([[IN_ARG:%.*]] : $*T):
+// CHECK:   destroy_addr [[IN_ARG]] : $*T
+// CHECK:   [[RESULT:%.*]] = tuple ()
+// CHECK:   return [[RESULT]] : $()
+
+// -- Back deployment thunk for genericFuncWithOwnedParam(_:)
+// CHECK-LABEL: sil non_abi [serialized] [thunk] [ossa] @$s11back_deploy25genericFuncWithOwnedParamyyxnlFTwb : $@convention(thin) <T> (@in T) -> ()
+// CHECK: bb0([[IN_ARG:%.*]] : $*T):
+// CHECK:   [[MAJOR:%.*]] = integer_literal $Builtin.Word, 10
+// CHECK:   [[MINOR:%.*]] = integer_literal $Builtin.Word, 52
+// CHECK:   [[PATCH:%.*]] = integer_literal $Builtin.Word, 0
+// CHECK:   [[OSVFN:%.*]] = function_ref @$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:   [[AVAIL:%.*]] = apply [[OSVFN]]([[MAJOR]], [[MINOR]], [[PATCH]]) : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:   cond_br [[AVAIL]], [[AVAIL_BB:bb[0-9]+]], [[UNAVAIL_BB:bb[0-9]+]]
+//
+// CHECK: [[UNAVAIL_BB]]:
+// CHECK:   [[FALLBACKFN:%.*]] = function_ref @$s11back_deploy25genericFuncWithOwnedParamyyxnlFTwB : $@convention(thin) <τ_0_0> (@in τ_0_0) -> ()
+// CHECK:   {{%.*}} = apply [[FALLBACKFN]]<T>([[IN_ARG]]) : $@convention(thin) <τ_0_0> (@in τ_0_0) -> ()
+// CHECK:   br [[RETURN_BB:bb[0-9]+]]
+//
+// CHECK: [[AVAIL_BB]]:
+// CHECK:   [[ORIGFN:%.*]] = function_ref @$s11back_deploy25genericFuncWithOwnedParamyyxnlF : $@convention(thin) <τ_0_0> (@in τ_0_0) -> ()
+// CHECK:   {{%.*}} = apply [[ORIGFN]]<T>([[IN_ARG]]) : $@convention(thin) <τ_0_0> (@in τ_0_0) -> ()
+// CHECK:   br [[RETURN_BB]]
+//
+// CHECK: [[RETURN_BB]]
+// CHECK-NOT: destroy_addr
+// CHECK:   [[RESULT:%.*]] = tuple ()
+// CHECK:   return [[RESULT]] : $()
+
+// -- Original definition of genericFuncWithOwnedParam(_:)
+// CHECK-LABEL: sil [available 10.52] [ossa] @$s11back_deploy25genericFuncWithOwnedParamyyxnlF : $@convention(thin) <T> (@in T) -> ()
+@_backDeploy(before: macOS 10.52)
+public func genericFuncWithOwnedParam<T>(_ t: __owned T) { }
+
+struct S {}
+
 // CHECK-LABEL: sil hidden [ossa] @$s11back_deploy6calleryyF : $@convention(thin) () -> ()
 func caller() {
-  // -- Verify the thunk is called
+  // -- Verify the thunks are called
   // CHECK: {{%.*}} = function_ref @$s11back_deploy11genericFuncyxxlFTwb : $@convention(thin) <τ_0_0> (@in_guaranteed τ_0_0) -> @out τ_0_0
-  _ = genericFunc(Int32(1))
+  _ = genericFunc(S())
+
+  // CHECK: {{%.*}} = function_ref @$s11back_deploy25genericFuncWithOwnedParamyyxnlFTwb : $@convention(thin) <τ_0_0> (@in τ_0_0) -> ()
+  genericFuncWithOwnedParam(S())
 }
diff --git a/test/attr/Inputs/BackDeployHelper.swift b/test/attr/Inputs/BackDeployHelper.swift
index 7aa5b7916f4e7..eaab7a3d231b8 100644
--- a/test/attr/Inputs/BackDeployHelper.swift
+++ b/test/attr/Inputs/BackDeployHelper.swift
@@ -35,7 +35,7 @@ public func v2APIsAreStripped() -> Bool {
 /// Describes types that can be appended to.
 public protocol Appendable {
   associatedtype Element
-  mutating func append(_ x: Element)
+  mutating func append(_ x: __owned Element)
 }
 
 /// Describes types that can be counted.
@@ -107,7 +107,7 @@ public func pleaseThrow(_ shouldThrow: Bool) throws -> Bool {
 @_backDeploy(before: BackDeploy 2.0)
 public func genericAppend<T: Appendable>(
   _ a: inout T,
-  _ x: T.Element
+  _ x: __owned T.Element
 ) {
   return a.append(x)
 }