diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -1175,15 +1175,29 @@
         if (CurrentToken->isOneOf(tok::star, tok::amp))
           CurrentToken->setType(TT_PointerOrReference);
         consumeToken();
-        if (CurrentToken && CurrentToken->is(tok::comma) &&
+        if (!CurrentToken)
+          continue;
+        if (CurrentToken->is(tok::comma) &&
             CurrentToken->Previous->isNot(tok::kw_operator)) {
           break;
         }
-        if (CurrentToken && CurrentToken->Previous->isOneOf(
-                                TT_BinaryOperator, TT_UnaryOperator, tok::comma,
-                                tok::star, tok::arrow, tok::amp, tok::ampamp)) {
+        if (CurrentToken->Previous->isOneOf(TT_BinaryOperator, TT_UnaryOperator,
+                                            tok::comma, tok::star, tok::arrow,
+                                            tok::amp, tok::ampamp)) {
           CurrentToken->Previous->setType(TT_OverloadedOperator);
         }
+        // User defined literal without a space.
+        if (CurrentToken->Previous->is(tok::string_literal) &&
+            CurrentToken->Previous->TokenText.startswith("\"\"")) {
+          CurrentToken->Previous->setType(TT_OverloadedOperator);
+        }
+        // User defined literal with a space.
+        if (CurrentToken->Previous->is(tok::string_literal) &&
+            CurrentToken->Previous->TokenText == "\"\"" &&
+            CurrentToken->is(tok::identifier)) {
+          CurrentToken->Previous->setType(TT_OverloadedOperator);
+          CurrentToken->setType(TT_OverloadedOperator);
+        }
       }
       if (CurrentToken && CurrentToken->is(tok::l_paren))
         CurrentToken->setType(TT_OverloadedOperatorLParen);
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -10153,6 +10153,14 @@
   // verifyFormat("void f() { operator*(a & a); }");
   // verifyFormat("void f() { operator&(a, b * b); }");
 
+  verifyFormat("void f() { return operator()(x) * b; }");
+  verifyFormat("void f() { return operator[](x) * b; }");
+  verifyFormat("void f() { return operator\"\"_a(x) * b; }");
+  verifyFormat("void f() { return operator\"\" _a(x) * b; }");
+  verifyFormat("void f() { return operator\"\"s(x) * b; }");
+  verifyFormat("void f() { return operator\"\" s(x) * b; }");
+  verifyFormat("void f() { return operator\"\"if(x) * b; }");
+
   verifyFormat("::operator delete(foo);");
   verifyFormat("::operator new(n * sizeof(foo));");
   verifyFormat("foo() { ::operator delete(foo); }");
diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
--- a/clang/unittests/Format/TokenAnnotatorTest.cpp
+++ b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -376,6 +376,66 @@
   EXPECT_TOKEN(Tokens[11], tok::amp, TT_PointerOrReference);
 }
 
+TEST_F(TokenAnnotatorTest, UnderstandsOverloadedOperators) {
+  auto Tokens = annotate("x.operator+()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::plus, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator=()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::equal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator+=()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::plusequal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator,()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::comma, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator()()");
+  ASSERT_EQ(Tokens.size(), 8u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::l_paren, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::r_paren, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[5], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator[]()");
+  ASSERT_EQ(Tokens.size(), 8u) << Tokens;
+  // EXPECT_TOKEN(Tokens[3], tok::l_square, TT_OverloadedOperator);
+  // EXPECT_TOKEN(Tokens[4], tok::r_square, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[5], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator\"\"_a()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::string_literal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator\"\" _a()");
+  ASSERT_EQ(Tokens.size(), 8u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::string_literal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::identifier, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[5], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator\"\"_long_literal()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::string_literal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator\"\" _long_literal()");
+  ASSERT_EQ(Tokens.size(), 8u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::string_literal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::identifier, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[5], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator\"\"if()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::string_literal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator\"\"s()");
+  ASSERT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::string_literal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+  Tokens = annotate("x.operator\"\" s()");
+  ASSERT_EQ(Tokens.size(), 8u) << Tokens;
+  EXPECT_TOKEN(Tokens[3], tok::string_literal, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[4], tok::identifier, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[5], tok::l_paren, TT_OverloadedOperatorLParen);
+}
+
 TEST_F(TokenAnnotatorTest, UnderstandsRequiresClausesAndConcepts) {
   auto Tokens = annotate("template <typename T>\n"
                          "concept C = (Foo && Bar) && (Bar && Baz);");