diff --git a/lib/ClangImporter/SwiftifyDecl.cpp b/lib/ClangImporter/SwiftifyDecl.cpp
index 9a7770117092f..6d5b40bb655ce 100644
--- a/lib/ClangImporter/SwiftifyDecl.cpp
+++ b/lib/ClangImporter/SwiftifyDecl.cpp
@@ -414,13 +414,24 @@ static bool swiftifyImpl(ClangImporter::Implementation &Self,
     }
 
     bool isClangInstanceMethod =
-        isa<clang::CXXMethodDecl>(ClangDecl) &&
-        !isa<clang::CXXConstructorDecl>(ClangDecl) &&
-        cast<clang::CXXMethodDecl>(ClangDecl)->isInstance();
-    size_t swiftNumParams = MappedDecl->getParameters()->size() -
-                            (ClangDecl->isVariadic() ? 1 : 0);
-    ASSERT((MappedDecl->isImportAsInstanceMember() == isClangInstanceMethod) ==
-           (getNumParams(ClangDecl) == swiftNumParams));
+        (isa<clang::CXXMethodDecl>(ClangDecl) &&
+         !isa<clang::CXXConstructorDecl>(ClangDecl) &&
+         cast<clang::CXXMethodDecl>(ClangDecl)->isInstance()) ||
+        (isa<clang::ObjCMethodDecl>(ClangDecl) &&
+         cast<clang::ObjCMethodDecl>(ClangDecl)->isInstanceMethod());
+
+    size_t swiftNumParams = MappedDecl->getParameters()->size();
+    if (MappedDecl->isInstanceMember() && !isClangInstanceMethod) {
+      ASSERT(MappedDecl->isImportAsInstanceMember());
+      swiftNumParams += 1;
+    }
+    if (getNumParams(ClangDecl) != swiftNumParams) {
+      DLOG("mismatching parameter lists");
+      assert(ClangDecl->isVariadic() ||
+             MappedDecl->getForeignErrorConvention().has_value() ||
+             MappedDecl->getForeignAsyncConvention().has_value());
+      return false;
+    }
 
     size_t selfParamIndex = MappedDecl->isImportAsInstanceMember()
                                 ? MappedDecl->getSelfIndex()
@@ -531,6 +542,9 @@ class SwiftifyProtocolInfoPrinter : public SwiftifyInfoPrinter {
   void printMethodSignature(const FuncDecl *Method) {
     auto options =
         PrintOptions::printForDiagnostics(AccessLevel::Private, true);
+    for (const auto *attr : Method->getAttrs()) {
+      options.ExcludeAttrList.push_back(attr->getKind());
+    }
     StreamPrinter printer(out);
     Method->print(printer, options);
   }
diff --git a/test/Interop/C/swiftify-import/Inputs/counted-by.h b/test/Interop/C/swiftify-import/Inputs/counted-by.h
index 2b855eeffc430..5fde5abf2d285 100644
--- a/test/Interop/C/swiftify-import/Inputs/counted-by.h
+++ b/test/Interop/C/swiftify-import/Inputs/counted-by.h
@@ -62,3 +62,5 @@ void hexLiteral(int * __counted_by(0xfa) p);
 void binaryLiteral(int * __counted_by(0b10) p);
 
 void octalLiteral(int * __counted_by(0777) p);
+
+void variadic(int len, int * __counted_by(len) p, ...);
diff --git a/test/Interop/C/swiftify-import/counted-by-no-swiftify.swift b/test/Interop/C/swiftify-import/counted-by-no-swiftify.swift
index ff565150f4126..7948eeb80f6a5 100644
--- a/test/Interop/C/swiftify-import/counted-by-no-swiftify.swift
+++ b/test/Interop/C/swiftify-import/counted-by-no-swiftify.swift
@@ -16,3 +16,4 @@
 // CHECK-NOT: @_alwaysEmitIntoClient {{.*}} longLiteral
 // CHECK-NOT: @_alwaysEmitIntoClient {{.*}} sizeofType
 // CHECK-NOT: @_alwaysEmitIntoClient {{.*}} sizeofParam
+// CHECK-NOT: @_alwaysEmitIntoClient {{.*}} variadic
diff --git a/test/Interop/ObjC/swiftify-import/Inputs/objc-no-swiftify.h b/test/Interop/ObjC/swiftify-import/Inputs/objc-no-swiftify.h
index 4b01f0e94f4f7..0ee95be5d6312 100644
--- a/test/Interop/ObjC/swiftify-import/Inputs/objc-no-swiftify.h
+++ b/test/Interop/ObjC/swiftify-import/Inputs/objc-no-swiftify.h
@@ -7,3 +7,14 @@
 void autoreleaseParam(SomeClass * __autoreleasing * __counted_by(len) p, int len); // expected-note{{declared here}}
 
 SomeClass * __autoreleasing * __counted_by(len) autoreleaseReturn(int len);
+
+@interface NSError
+@end
+
+@interface NSData
+@end
+
+@protocol Foo
+- (void)errorAsTry:(int) len : (int * __counted_by(len)) p error:(NSError * *) error;
+- (void)completionHandlerAsAsync:(int) len : (int * __counted_by(len)) p completionHandler:(void (^)(NSData * data, NSError *)) completionHandler;
+@end
diff --git a/test/Interop/ObjC/swiftify-import/objc-no-swiftify.swift b/test/Interop/ObjC/swiftify-import/objc-no-swiftify.swift
index 5c918bc4bec5c..4563154e203ed 100644
--- a/test/Interop/ObjC/swiftify-import/objc-no-swiftify.swift
+++ b/test/Interop/ObjC/swiftify-import/objc-no-swiftify.swift
@@ -7,8 +7,7 @@
 
 import NoSwiftifyClang
 
-// CHECK-NOT: @_alwaysEmitIntoClient @_disfavoredOverload public func callAutoreleaseParam
-// CHECK-NOT: @_alwaysEmitIntoClient @_disfavoredOverload public func callAutoreleaseReturn
+// CHECK-NOT: @_alwaysEmitIntoClient @_disfavoredOverload
 
 public func callAutoreleaseParam(_ p: UnsafeMutableBufferPointer<SomeClass>) {
     // expected-error@+2{{missing argument for parameter #2 in call}}
@@ -19,4 +18,14 @@ public func callAutoreleaseParam(_ p: UnsafeMutableBufferPointer<SomeClass>) {
 public func callAutoreleaseReturn() {
     // expected-error@+1{{cannot convert value of type 'AutoreleasingUnsafeMutablePointer<SomeClass?>?' to specified type 'UnsafeMutableBufferPointer<SomeClass>'}}
     let p: UnsafeMutableBufferPointer<SomeClass> = autoreleaseReturn(10)
-}
\ No newline at end of file
+}
+
+public func callErrorAsTry(_ x: Foo, _ p: UnsafeMutablePointer<CInt>, _ error: AutoreleasingUnsafeMutablePointer<NSError?>) {
+  x.error(asTry: 10, p, error: error)
+}
+
+public func callCompletionHandlerAsAsync(_ x: Foo, _ p: UnsafeMutablePointer<CInt>) {
+  x.completionHandler(asAsync: 10, p, completionHandler: { (a: NSData?, b: NSError?) in
+    print("asdf")
+  })
+}