Index: clang/lib/Sema/SemaLookup.cpp
===================================================================
--- clang/lib/Sema/SemaLookup.cpp
+++ clang/lib/Sema/SemaLookup.cpp
@@ -3634,14 +3634,17 @@
       bool Visible = false;
       for (D = D->getMostRecentDecl(); D;
            D = cast_or_null<NamedDecl>(D->getPreviousDecl())) {
-        if (D->getIdentifierNamespace() & Decl::IDNS_Ordinary) {
-          if (isVisible(D)) {
+        // We check the friend case first because in case of MSVC compatibility
+        // a friend declaration is also flagged as Ordinary but we don't want
+        // it to be visible outside its associated class.
+        if (D->getFriendObjectKind()) {
+          auto *RD = cast<CXXRecordDecl>(D->getLexicalDeclContext());
+          if (AssociatedClasses.count(RD) && isVisible(D)) {
             Visible = true;
             break;
           }
-        } else if (D->getFriendObjectKind()) {
-          auto *RD = cast<CXXRecordDecl>(D->getLexicalDeclContext());
-          if (AssociatedClasses.count(RD) && isVisible(D)) {
+        } else if (D->getIdentifierNamespace() & Decl::IDNS_Ordinary) {
+          if (isVisible(D)) {
             Visible = true;
             break;
           }
Index: clang/test/SemaCXX/ms-friend-function-decl.cpp
===================================================================
--- clang/test/SemaCXX/ms-friend-function-decl.cpp
+++ clang/test/SemaCXX/ms-friend-function-decl.cpp
@@ -1,9 +1,5 @@
-// RUN: %clang_cc1 -std=c++03 -fms-compatibility -fsyntax-only -verify %s
-// RUN: %clang_cc1 -std=c++17 -fms-compatibility -fsyntax-only -verify %s
-// RUN: %clang_cc1 -std=c++20 -fms-compatibility -fsyntax-only -verify=modern %s
-#if __cplusplus < 202002L
-// expected-no-diagnostics
-#endif
+// RUN: %clang_cc1 -std=c++17 -fms-compatibility -fsyntax-only -verify=expected %s
+// RUN: %clang_cc1 -std=c++20 -fms-compatibility -fsyntax-only -verify=modern,expected %s
 
 namespace ns {
 
@@ -43,3 +39,43 @@
 
 void funGlob() {
 }
+
+// At some point, considering friend declaration as full declarations broke ADL detection.
+// The following test checks that the friend declaration is only visible inside the class it's declared in.
+namespace check_adl {
+template <typename T>
+struct A {};
+
+struct NotADLVisible {
+  template <typename T>
+  friend constexpr bool operator==(A<T>, NotADLVisible) noexcept {
+    static_assert(sizeof(T) < 0, "This should never be instantiated");
+    return false;
+  }
+
+  constexpr NotADLVisible(int) {}
+};
+} // namespace check_adl
+
+void shouldNotSeeAnyOperator() {
+  bool b = check_adl::A<int>() == 2; // expected-error {{invalid operands to binary expression ('check_adl::A<int>' and 'int')}}
+}
+
+// Check that we don't break the case of a function that is both visible to ADL and a friend
+namespace check_adl_compliant {
+struct A {};
+
+struct B {
+  friend constexpr bool operator==(A, B) noexcept;
+
+  constexpr B(int) {}
+};
+
+constexpr bool operator==(check_adl_compliant::A, check_adl_compliant::B) noexcept {
+  return false;
+}
+} // namespace check_adl_compliant
+
+void shouldSeeTheOperator() {
+  bool b = check_adl_compliant::A() == 2;
+}