diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 50d3bbbc97e91..c37c3d586de7b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -128,7 +128,9 @@ Improvements to Clang's diagnostics
   which are supposed to only exist once per program, but may get duplicated when
   built into a shared library.
 - Fixed a bug where Clang's Analysis did not correctly model the destructor behavior of ``union`` members (#GH119415).
-
+- Clang now provides a diagnostic note for function-like macros that are
+  missing the required parentheses (#GH123038).
+  
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index bcae9e9f30093..bafc2308f522f 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5961,6 +5961,8 @@ def err_fold_expression_limit_exceeded: Error<
   "instantiating fold expression with %0 arguments exceeded expression nesting "
   "limit of %1">, DefaultFatal, NoSFINAE;
 
+def note_function_like_macro_requires_parens
+    : Note<"'%0' defined here as a function-like macro">;
 def err_unexpected_typedef : Error<
   "unexpected type name %0: expected expression">;
 def err_unexpected_namespace : Error<
@@ -10855,6 +10857,8 @@ def err_undeclared_use_suggest : Error<
   "use of undeclared %0; did you mean %1?">;
 def err_undeclared_var_use_suggest : Error<
   "use of undeclared identifier %0; did you mean %1?">;
+def err_undeclared_var_use_suggest_func_like_macro : Error<
+  "'%0' is defined as an object-like macro; did you mean '%0(...)'?">;
 def err_no_template : Error<"no template named %0">;
 def err_no_template_suggest : Error<"no template named %0; did you mean %1?">;
 def err_no_member_template : Error<"no template named %0 in %1">;
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 3cd4010740d19..c3b5c705178a1 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -2347,6 +2347,28 @@ Sema::BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
   return E;
 }
 
+// Diagnose when a macro cannot be expanded because it's a function-like macro
+// being used as an object-like macro. Returns true if a diagnostic is emitted.
+static bool diagnoseFunctionLikeMacro(Sema &SemaRef, DeclarationName Name,
+                                      SourceLocation TypoLoc) {
+
+  if (IdentifierInfo *II = Name.getAsIdentifierInfo()) {
+    if (II->hasMacroDefinition()) {
+      MacroInfo *MI = SemaRef.PP.getMacroInfo(II);
+      if (MI && MI->isFunctionLike()) {
+        SemaRef.Diag(TypoLoc,
+                     diag::err_undeclared_var_use_suggest_func_like_macro)
+            << II ->getName();
+        SemaRef.Diag(MI->getDefinitionLoc(),
+                     diag::note_function_like_macro_requires_parens)
+            << II->getName();
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
 void
 Sema::DecomposeUnqualifiedId(const UnqualifiedId &Id,
                              TemplateArgumentListInfo &Buffer,
@@ -2382,6 +2404,8 @@ static void emitEmptyLookupTypoDiagnostic(
     if (Ctx)
       SemaRef.Diag(TypoLoc, diag::err_no_member) << Typo << Ctx
                                                  << SS.getRange();
+    else if (diagnoseFunctionLikeMacro(SemaRef, Typo, TypoLoc))
+      return;
     else
       SemaRef.Diag(TypoLoc, DiagnosticID) << Typo;
     return;
@@ -2624,6 +2648,9 @@ bool Sema::DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
   }
   R.clear();
 
+  if (diagnoseFunctionLikeMacro(SemaRef, Name, R.getNameLoc()))
+    return true;
+
   // Emit a special diagnostic for failed member lookups.
   // FIXME: computing the declaration context might fail here (?)
   if (!SS.isEmpty()) {
diff --git a/clang/test/Preprocessor/macro_with_initializer_list.cpp b/clang/test/Preprocessor/macro_with_initializer_list.cpp
index 40f53164b263d..d9e653106d4a1 100644
--- a/clang/test/Preprocessor/macro_with_initializer_list.cpp
+++ b/clang/test/Preprocessor/macro_with_initializer_list.cpp
@@ -133,7 +133,8 @@ void test_NE() {
 // CHECK: fix-it:"{{.*}}macro_with_initializer_list.cpp":{110:9-110:9}:"("
 // CHECK: fix-it:"{{.*}}macro_with_initializer_list.cpp":{110:32-110:32}:")"
 
-#define INIT(var, init) Foo var = init; // expected-note 3{{defined here}}
+#define INIT(var, init) Foo var = init; // expected-note 3{{macro 'INIT' defined here}}
+// expected-note@-1 2{{'INIT' defined here as a function-like macro}}
 // Can't use an initializer list as a macro argument.  The commas in the list
 // will be interpretted as argument separaters and adding parenthesis will
 // make it no longer an initializer list.
@@ -149,22 +150,23 @@ void test() {
   // Can't be fixed by parentheses.
   INIT(e, {1, 2, 3});
   // expected-error@-1 {{too many arguments provided}}
-  // expected-error@-2 {{use of undeclared identifier}}
+  // expected-error@-2 {{'INIT' is defined as an object-like macro; did you mean 'INIT(...)'?}}
   // expected-note@-3 {{cannot use initializer list at the beginning of a macro argument}}
 
   // Can't be fixed by parentheses.
   INIT(e, {1, 2, 3} + {1, 2, 3});
   // expected-error@-1 {{too many arguments provided}}
-  // expected-error@-2 {{use of undeclared identifier}}
+  // expected-error@-2 {{'INIT' is defined as an object-like macro; did you mean 'INIT(...)'?}}
   // expected-note@-3 {{cannot use initializer list at the beginning of a macro argument}}
 }
 
-// CHECK: fix-it:"{{.*}}macro_with_initializer_list.cpp":{145:11-145:11}:"("
-// CHECK: fix-it:"{{.*}}macro_with_initializer_list.cpp":{145:23-145:23}:")"
+// CHECK: fix-it:"{{.*}}macro_with_initializer_list.cpp":{146:11-146:11}:"("
+// CHECK: fix-it:"{{.*}}macro_with_initializer_list.cpp":{146:23-146:23}:")"
 
 #define M(name,a,b,c,d,e,f,g,h,i,j,k,l) \
   Foo name = a + b + c + d + e + f + g + h + i + j + k + l;
 // expected-note@-2 2{{defined here}}
+// expected-note@-3 {{'M' defined here as a function-like macro}}
 void test2() {
   M(F1, Foo(), Foo(), Foo(), Foo(), Foo(), Foo(),
         Foo(), Foo(), Foo(), Foo(), Foo(), Foo());
@@ -177,6 +179,6 @@ void test2() {
   M(F3, {1,2,3}, {1,2,3}, {1,2,3}, {1,2,3}, {1,2,3}, {1,2,3},
         {1,2,3}, {1,2,3}, {1,2,3}, {1,2,3}, {1,2,3}, {1,2,3});
   // expected-error@-2 {{too many arguments provided}}
-  // expected-error@-3 {{use of undeclared identifier}}
+  // expected-error@-3 {{'M' is defined as an object-like macro; did you mean 'M(...)'?}}
   // expected-note@-4 {{cannot use initializer list at the beginning of a macro argument}}
 }
diff --git a/clang/test/Sema/typo-correction.c b/clang/test/Sema/typo-correction.c
index 4157207a9ac42..e000ecdf234e3 100644
--- a/clang/test/Sema/typo-correction.c
+++ b/clang/test/Sema/typo-correction.c
@@ -114,3 +114,25 @@ void PR40286_3(int the_value) {
 void PR40286_4(int the_value) { // expected-note {{'the_value' declared here}}
   PR40286_h(the_value, the_value, the_walue); // expected-error {{use of undeclared identifier 'the_walue'; did you mean 'the_value'?}}
 }
+
+#define FOO1() 10
+// expected-note@-1 4 {{'FOO1' defined here as a function-like macro}}
+
+int x = FOO1; // expected-error {{'FOO1' is defined as an object-like macro; did you mean 'FOO1(...)'?}}
+
+void test3() {
+  int iter = FOO1;
+  // expected-error@-1 {{'FOO1' is defined as an object-like macro; did you mean 'FOO1(...)'?}}
+}
+
+void bar(int);
+
+void test4() {
+    int FOO; // expected-note {{'FOO' declared here}}
+    int x = FOO1; // expected-error {{use of undeclared identifier 'FOO1'; did you mean 'FOO'?}}
+}
+
+void test5() {
+    FOO1 + 1; // expected-error {{'FOO1' is defined as an object-like macro; did you mean 'FOO1(...)'?}}
+    bar(FOO1); // expected-error {{'FOO1' is defined as an object-like macro; did you mean 'FOO1(...)'?}}
+}