diff --git a/clang/include/clang/AST/DeclObjC.h b/clang/include/clang/AST/DeclObjC.h
--- a/clang/include/clang/AST/DeclObjC.h
+++ b/clang/include/clang/AST/DeclObjC.h
@@ -1955,6 +1955,13 @@
   const ObjCIvarDecl *getNextIvar() const { return NextIvar; }
   void setNextIvar(ObjCIvarDecl *ivar) { NextIvar = ivar; }
 
+  ObjCIvarDecl *getCanonicalDecl() override {
+    return cast<ObjCIvarDecl>(FieldDecl::getCanonicalDecl());
+  }
+  const ObjCIvarDecl *getCanonicalDecl() const {
+    return const_cast<ObjCIvarDecl *>(this)->getCanonicalDecl();
+  }
+
   void setAccessControl(AccessControl ac) { DeclAccess = ac; }
 
   AccessControl getAccessControl() const { return AccessControl(DeclAccess); }
diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -3404,6 +3404,7 @@
 uint64_t ASTContext::lookupFieldBitOffset(const ObjCInterfaceDecl *OID,
                                           const ObjCImplementationDecl *ID,
                                           const ObjCIvarDecl *Ivar) const {
+  Ivar = Ivar->getCanonicalDecl();
   const ObjCInterfaceDecl *Container = Ivar->getContainingInterface();
 
   // FIXME: We should eliminate the need to have ObjCImplementationDecl passed
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -3350,6 +3350,9 @@
     return ED->getASTContext().getLangOpts().CPlusPlus? ED->getDefinition()
                                                       : nullptr;
 
+  if (auto *OID = dyn_cast<ObjCInterfaceDecl>(DC))
+    return OID->getDefinition();
+
   // We can see the TU here only if we have no Sema object. In that case,
   // there's no TU scope to look in, so using the DC alone is sufficient.
   if (auto *TU = dyn_cast<TranslationUnitDecl>(DC))
diff --git a/clang/test/Modules/merge-objc-interface.m b/clang/test/Modules/merge-objc-interface.m
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/merge-objc-interface.m
@@ -0,0 +1,105 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: %clang_cc1 -emit-llvm -o %t/test.bc -F%t/Frameworks %t/test.m \
+// RUN:            -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache
+// RUN: %clang_cc1 -emit-llvm -o %t/test.bc -F%t/Frameworks %t/test-functions.m \
+// RUN:            -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache
+
+// Test a case when Objective-C interface ivars are present in two different modules.
+
+//--- Frameworks/Foundation.framework/Headers/Foundation.h
+@interface NSObject
+@end
+
+//--- Frameworks/Foundation.framework/Modules/module.modulemap
+framework module Foundation {
+  header "Foundation.h"
+  export *
+}
+
+//--- Frameworks/ObjCInterface.framework/Headers/ObjCInterface.h
+#import <Foundation/Foundation.h>
+@interface ObjCInterface : NSObject {
+@public
+  id _item;
+}
+@end
+
+@interface WithBitFields : NSObject {
+@public
+  int x: 3;
+  int y: 4;
+}
+@end
+
+//--- Frameworks/ObjCInterface.framework/Modules/module.modulemap
+framework module ObjCInterface {
+  header "ObjCInterface.h"
+  export *
+}
+
+//--- Frameworks/ObjCInterfaceCopy.framework/Headers/ObjCInterfaceCopy.h
+#import <Foundation/Foundation.h>
+@interface ObjCInterface : NSObject {
+@public
+  id _item;
+}
+@end
+
+@interface WithBitFields : NSObject {
+@public
+  int x: 3;
+  int y: 4;
+}
+@end
+
+// Inlined function present only in Copy.framework to make sure it uses decls from Copy module.
+__attribute__((always_inline)) void inlinedIVarAccessor(ObjCInterface *obj, WithBitFields *bitFields) {
+  obj->_item = 0;
+  bitFields->x = 0;
+}
+
+//--- Frameworks/ObjCInterfaceCopy.framework/Modules/module.modulemap
+framework module ObjCInterfaceCopy {
+  header "ObjCInterfaceCopy.h"
+  export *
+}
+
+//--- test.m
+#import <ObjCInterface/ObjCInterface.h>
+#import <ObjCInterfaceCopy/ObjCInterfaceCopy.h>
+
+@implementation ObjCInterface
+- (void)test:(id)item {
+  _item = item;
+}
+@end
+
+@implementation WithBitFields
+- (void)reset {
+  x = 0;
+  y = 0;
+}
+@end
+
+//--- test-functions.m
+#import <ObjCInterface/ObjCInterface.h>
+
+void testAccessIVar(ObjCInterface *obj, id item) {
+  obj->_item = item;
+}
+void testAccessBitField(WithBitFields *obj) {
+  obj->x = 0;
+}
+
+#import <ObjCInterfaceCopy/ObjCInterfaceCopy.h>
+
+void testAccessIVarLater(ObjCInterface *obj, id item) {
+  obj->_item = item;
+}
+void testAccessBitFieldLater(WithBitFields *obj) {
+  obj->y = 0;
+}
+void testInlinedFunction(ObjCInterface *obj, WithBitFields *bitFields) {
+  inlinedIVarAccessor(obj, bitFields);
+}