diff --git a/src/jshint.js b/src/jshint.js
index 187fa33694..4adbc44d4c 100644
--- a/src/jshint.js
+++ b/src/jshint.js
@@ -2800,10 +2800,12 @@ var JSHINT = (function() {
         }
       }
 
-      // it is a syntax error to have a regular argument after a default argument
+      // It is valid to have a regular argument after a default argument
+      // since undefined can be used for missing parameters. Still warn as it is
+      // a possible code smell.
       if (pastDefault) {
         if (state.tokens.next.id !== "=") {
-          error("E051", state.tokens.current);
+          error("W138", state.tokens.current);
         }
       }
       if (state.tokens.next.id === "=") {
diff --git a/src/messages.js b/src/messages.js
index 77aad4b887..8b2c91777b 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -62,11 +62,11 @@ var errors = {
   E044: null,
   E045: "Invalid for each loop.",
   E046: "A yield statement shall be within a generator function (with syntax: `function*`)",
-  E047: null, // Vacant
+  E047: null,
   E048: "{a} declaration not directly within block.",
   E049: "A {a} cannot be named '{b}'.",
   E050: "Mozilla requires the yield expression to be parenthesized here.",
-  E051: "Regular parameters cannot come after default parameters.",
+  E051: null,
   E052: "Unclosed template literal.",
   E053: "Export declaration must be in global scope.",
   E054: "Class properties must be methods. Expected '(' but instead saw '{a}'.",
@@ -217,7 +217,8 @@ var warnings = {
   W134: "The '{a}' option is only available when linting ECMAScript {b} code.",
   W135: "{a} may not be supported by non-browser environments.",
   W136: "'{a}' must be in function scope.",
-  W137: "Empty destructuring."
+  W137: "Empty destructuring.",
+  W138: "Regular parameters should not come after default parameters."
 };
 
 var info = {
diff --git a/tests/unit/core.js b/tests/unit/core.js
index 986a2d9e8d..40033fb29d 100644
--- a/tests/unit/core.js
+++ b/tests/unit/core.js
@@ -1438,7 +1438,7 @@ exports.testDefaultArguments = function (test) {
     .addError(14, "'bar' is not defined.")
     .addError(14, "'num3' was used before it was declared, which is illegal for 'param' variables.")
     .addError(15, "'num4' was used before it was declared, which is illegal for 'param' variables.")
-    .addError(18, "Regular parameters cannot come after default parameters.")
+    .addError(18, "Regular parameters should not come after default parameters.")
     .addError(27, "'c' is not defined.")
     .addError(33, "'d' was used before it was defined.")
     .addError(36, "'e' was used before it was declared, which is illegal for 'param' variables.")
@@ -1447,7 +1447,7 @@ exports.testDefaultArguments = function (test) {
   TestRun(test)
     .addError(14, "'num3' was used before it was declared, which is illegal for 'param' variables.")
     .addError(15, "'num4' was used before it was declared, which is illegal for 'param' variables.")
-    .addError(18, "Regular parameters cannot come after default parameters.")
+    .addError(18, "Regular parameters should not come after default parameters.")
     .addError(36, "'e' was used before it was declared, which is illegal for 'param' variables.")
     .test(src, { moz: true });
 
@@ -1461,7 +1461,7 @@ exports.testDefaultArguments = function (test) {
     .addError(15, "'default parameters' is only available in ES6 (use esnext option).")
     .addError(15, "'num4' was used before it was declared, which is illegal for 'param' variables.")
     .addError(18, "'default parameters' is only available in ES6 (use esnext option).")
-    .addError(18, "Regular parameters cannot come after default parameters.")
+    .addError(18, "Regular parameters should not come after default parameters.")
     .addError(26, "'default parameters' is only available in ES6 (use esnext option).")
     .addError(31, "'default parameters' is only available in ES6 (use esnext option).")
     .addError(33, "'default parameters' is only available in ES6 (use esnext option).")