Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -229,7 +229,19 @@
     }
 
     if (Left->is(TT_OverloadedOperatorLParen)) {
-      Contexts.back().IsExpression = false;
+      // Find the previous kw_operator token.
+      FormatToken *Prev = Left;
+      while (!Prev->is(tok::kw_operator)) {
+        Prev = Prev->Previous;
+        assert(Prev && "Expect a kw_operator prior to the OperatorLParen!");
+      }
+
+      // If faced with "a.operator*(argument)" or "a->operator*(argument)",
+      // i.e. the operator is called as a member function,
+      // then the argument must be an expression.
+      bool OperatorCalledAsMemberFunction =
+          Prev->Previous && Prev->Previous->isOneOf(tok::period, tok::arrow);
+      Contexts.back().IsExpression = OperatorCalledAsMemberFunction;
     } else if (Style.Language == FormatStyle::LK_JavaScript &&
                (Line.startsWith(Keywords.kw_type, tok::identifier) ||
                 Line.startsWith(tok::kw_export, Keywords.kw_type,
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -8274,6 +8274,16 @@
   verifyFormat("using A::operator+;");
   verifyFormat("inline A operator^(const A &lhs, const A &rhs) {}\n"
                "int i;");
+
+  // Calling an operator as a member function.
+  verifyFormat("void f() { a.operator*(); }");
+  verifyFormat("void f() { a.operator*(b & b); }");
+  verifyFormat("void f() { a->operator&(a * b); }");
+  verifyFormat("void f() { NS::a.operator+(*b * *b); }");
+  // TODO: Calling an operator as a non-member function is hard to distinguish.
+  // https://llvm.org/PR50629
+  // verifyFormat("void f() { operator*(a & a); }");
+  // verifyFormat("void f() { operator&(a, b * b); }");
 }
 
 TEST_F(FormatTest, UnderstandsFunctionRefQualification) {
@@ -8761,6 +8771,13 @@
                "operator()() && {}");
   verifyGoogleFormat("template <typename T>\n"
                      "auto x() & -> int {}");
+
+  // Should be binary operators when used as an argument expression (overloaded
+  // operator invoked as a member function).
+  verifyFormat("void f() { a.operator()(a * a); }");
+  verifyFormat("void f() { a->operator()(a & a); }");
+  verifyFormat("void f() { a.operator()(*a & *a); }");
+  verifyFormat("void f() { a->operator()(*a * *a); }");
 }
 
 TEST_F(FormatTest, UnderstandsAttributes) {