diff --git a/clang/lib/CodeGen/CGObjCGNU.cpp b/clang/lib/CodeGen/CGObjCGNU.cpp
--- a/clang/lib/CodeGen/CGObjCGNU.cpp
+++ b/clang/lib/CodeGen/CGObjCGNU.cpp
@@ -3512,19 +3512,6 @@
   ClassMethods.insert(ClassMethods.begin(), OID->classmeth_begin(),
       OID->classmeth_end());
 
-  // Collect the same information about synthesized properties, which don't
-  // show up in the instance method lists.
-  for (auto *propertyImpl : OID->property_impls())
-    if (propertyImpl->getPropertyImplementation() ==
-        ObjCPropertyImplDecl::Synthesize) {
-      auto addPropertyMethod = [&](const ObjCMethodDecl *accessor) {
-        if (accessor)
-          InstanceMethods.push_back(accessor);
-      };
-      addPropertyMethod(propertyImpl->getGetterMethodDecl());
-      addPropertyMethod(propertyImpl->getSetterMethodDecl());
-    }
-
   llvm::Constant *Properties = GeneratePropertyList(OID, ClassDecl);
 
   // Collect the names of referenced protocols
diff --git a/clang/test/CodeGenObjC/gnu-method-only-once.m b/clang/test/CodeGenObjC/gnu-method-only-once.m
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenObjC/gnu-method-only-once.m
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-freebsd -S -emit-llvm -fobjc-runtime=gnustep-2.0 -o - %s | FileCheck %s -check-prefix=CHECK-NEW
+// RUN: %clang_cc1 -triple x86_64-unknown-freebsd -S -emit-llvm -fobjc-runtime=gnustep-1.8 -o - %s | FileCheck %s -check-prefix=CHECK-OLD
+
+// Clang 9 or 10 changed the handling of method lists so that methods provided
+// from synthesised properties showed up in the method list, where previously
+// CGObjCGNU had to collect them and merge them.  One of the places where this
+// merging happened was missed in the move and so we ended up emitting two
+// copies of method metadata for declared properties.
+
+// This class has only instance properties and only one pair of synthesized
+// methods from the property and so we should synthesize only one method list,
+// with precisely two methods on it.
+@interface X
+@property (retain) id iProp;
+@end
+
+@implementation X
+@synthesize iProp;
+@end
+
+// Check that the method list has precisely 2 methods.
+// CHECK-NEW: @.objc_method_list = internal global { i8*, i32, i64, [2 x
+// CHECK-OLD: @.objc_method_list = internal global { i8*, i32, [2 x