Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -5751,9 +5751,11 @@
   if (!S.checkStringLiteralArgumentAttr(AL, 0, BT))
     return;
 
-  // Don't duplicate annotations that are already set.
-  if (D->hasAttr<SwiftBridgeAttr>()) {
-    S.Diag(AL.getLoc(), diag::warn_duplicate_attribute) << AL;
+  // Warn about duplicate attributes if they have different arguments, but drop
+  // any duplicate attributes regardless.
+  if (const auto *Other = D->getAttr<SwiftBridgeAttr>()) {
+    if (Other->getSwiftType() != BT)
+      S.Diag(AL.getLoc(), diag::warn_duplicate_attribute) << AL;
     return;
   }
 
Index: clang/test/SemaObjC/attr-swift_bridge.m
===================================================================
--- clang/test/SemaObjC/attr-swift_bridge.m
+++ clang/test/SemaObjC/attr-swift_bridge.m
@@ -31,3 +31,8 @@
 typedef NSArray *NSArrayAlias __attribute__((__swift_bridge__("ArrayAlias")));
 
 struct __attribute__((__swift_bridge__("StructT"))) T {};
+
+// Duplicate attributes with the same arguments are fine.
+struct __attribute__((swift_bridge("foo"), swift_bridge("foo"))) S;
+// Duplicate attributes with different arguments are not.
+struct __attribute__((swift_bridge("foo"), swift_bridge("bar"))) S; // expected-warning {{attribute 'swift_bridge' is already applied with different arguments}}