Index: clang-tidy/readability/RedundantStringInitCheck.cpp
===================================================================
--- clang-tidy/readability/RedundantStringInitCheck.cpp
+++ clang-tidy/readability/RedundantStringInitCheck.cpp
@@ -61,7 +61,8 @@
                         hasInitializer(
                             expr(anyOf(EmptyStringCtorExpr,
                                        EmptyStringCtorExprWithTemporaries))
-                            .bind("expr"))))
+                            .bind("expr"))),
+                unless(parmVarDecl()))
           .bind("decl"),
       this);
 }
Index: test/clang-tidy/readability-redundant-string-init.cpp
===================================================================
--- test/clang-tidy/readability-redundant-string-init.cpp
+++ test/clang-tidy/readability-redundant-string-init.cpp
@@ -131,3 +131,10 @@
 
   std::string d = "u", e = "u", f = "u";
 }
+
+// These cases should not generate warnings.
+extern void Param1(std::string param = "");
+extern void Param2(const std::string& param = "");
+void Param3(std::string param = "") {}
+void Param4(STRING param = "") {}
+