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
@@ -310,9 +310,14 @@
       // 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;
+      // If faced with "operator+(argument)", i.e. the operator is called as
+      // a free function, then the argument is an expression only if the current
+      // line can't be a declaration.
+      bool IsOperatorCallSite =
+          (Prev->Previous &&
+           Prev->Previous->isOneOf(tok::period, tok::arrow)) ||
+          (!Line.MustBeDeclaration && !Line.InMacroBody);
+      Contexts.back().IsExpression = IsOperatorCallSite;
     } else if (OpeningParen.is(TT_VerilogInstancePortLParen)) {
       Contexts.back().IsExpression = true;
       Contexts.back().ContextType = Context::VerilogInstancePortList;
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
@@ -11580,6 +11580,14 @@
                    "  }",
                    getLLVMStyleWithColumns(50)));
 
+// FIXME: We should be able to figure out this is an operator call
+#if 0
+  verifyFormat("#define FOO             \\\n"
+               "  void foo() {          \\\n"
+               "    operator+(a * b);   \\\n"
+               "  }", getLLVMStyleWithColumns(25));
+#endif
+
   // FIXME: We cannot handle this case yet; we might be able to figure out that
   // foo<x> d > v; doesn't make sense.
   verifyFormat("foo<a<b && c> d> v;");
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
@@ -668,6 +668,33 @@
   EXPECT_TOKEN(Tokens[2], tok::l_paren, TT_OverloadedOperator);
   EXPECT_TOKEN(Tokens[3], tok::r_paren, TT_OverloadedOperator);
   EXPECT_TOKEN(Tokens[4], tok::l_paren, TT_OverloadedOperatorLParen);
+
+  Tokens = annotate("class Foo {\n"
+                    "  int operator+(a* b);\n"
+                    "}");
+  ASSERT_EQ(Tokens.size(), 14u) << Tokens;
+  EXPECT_TOKEN(Tokens[4], tok::kw_operator, TT_FunctionDeclarationName);
+  EXPECT_TOKEN(Tokens[5], tok::plus, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[6], tok::l_paren, TT_OverloadedOperatorLParen);
+  EXPECT_TOKEN(Tokens[8], tok::star, TT_PointerOrReference);
+
+  Tokens = annotate("void foo() {\n"
+                    "  operator+(a * b);\n"
+                    "}");
+  ASSERT_EQ(Tokens.size(), 15u) << Tokens;
+  EXPECT_TOKEN(Tokens[6], tok::plus, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[7], tok::l_paren, TT_OverloadedOperatorLParen);
+  EXPECT_TOKEN(Tokens[9], tok::star, TT_BinaryOperator);
+
+  Tokens = annotate("class Foo {\n"
+                    "  void foo() {\n"
+                    "    operator+(a * b);\n"
+                    "  }\n"
+                    "}");
+  ASSERT_EQ(Tokens.size(), 19u) << Tokens;
+  EXPECT_TOKEN(Tokens[9], tok::plus, TT_OverloadedOperator);
+  EXPECT_TOKEN(Tokens[10], tok::l_paren, TT_OverloadedOperatorLParen);
+  EXPECT_TOKEN(Tokens[12], tok::star, TT_BinaryOperator);
 }
 
 TEST_F(TokenAnnotatorTest, OverloadedOperatorInTemplate) {