diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index e516a6319ec..acab10a9ac3 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -18225,9 +18225,6 @@ namespace ts {
                     if (parameter.dotDotDotToken) {
                         return grammarErrorOnNode(parameter.dotDotDotToken, Diagnostics.A_set_accessor_cannot_have_rest_parameter);
                     }
-                    else if (parameter.flags & NodeFlags.Modifier) {
-                        return grammarErrorOnNode(accessor.name, Diagnostics.A_parameter_property_is_only_allowed_in_a_constructor_implementation);
-                    }
                     else if (parameter.questionToken) {
                         return grammarErrorOnNode(parameter.questionToken, Diagnostics.A_set_accessor_cannot_have_an_optional_parameter);
                     }
diff --git a/tests/baselines/reference/accessorParameterAccessibilityModifier.errors.txt b/tests/baselines/reference/accessorParameterAccessibilityModifier.errors.txt
index fad1d8ff10a..3036e734105 100644
--- a/tests/baselines/reference/accessorParameterAccessibilityModifier.errors.txt
+++ b/tests/baselines/reference/accessorParameterAccessibilityModifier.errors.txt
@@ -1,20 +1,14 @@
-tests/cases/compiler/accessorParameterAccessibilityModifier.ts(3,9): error TS2369: A parameter property is only allowed in a constructor implementation.
 tests/cases/compiler/accessorParameterAccessibilityModifier.ts(3,11): error TS2369: A parameter property is only allowed in a constructor implementation.
-tests/cases/compiler/accessorParameterAccessibilityModifier.ts(4,16): error TS2369: A parameter property is only allowed in a constructor implementation.
 tests/cases/compiler/accessorParameterAccessibilityModifier.ts(4,18): error TS2369: A parameter property is only allowed in a constructor implementation.
 
 
-==== tests/cases/compiler/accessorParameterAccessibilityModifier.ts (4 errors) ====
+==== tests/cases/compiler/accessorParameterAccessibilityModifier.ts (2 errors) ====
     
     class C {
         set X(public v) { }
-            ~
-!!! error TS2369: A parameter property is only allowed in a constructor implementation.
               ~~~~~~~~
 !!! error TS2369: A parameter property is only allowed in a constructor implementation.
         static set X(public v2) { }
-                   ~
-!!! error TS2369: A parameter property is only allowed in a constructor implementation.
                      ~~~~~~~~~
 !!! error TS2369: A parameter property is only allowed in a constructor implementation.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/parserMemberAccessorDeclaration15.errors.txt b/tests/baselines/reference/parserMemberAccessorDeclaration15.errors.txt
index f76264f6090..cba1e1fee92 100644
--- a/tests/baselines/reference/parserMemberAccessorDeclaration15.errors.txt
+++ b/tests/baselines/reference/parserMemberAccessorDeclaration15.errors.txt
@@ -1,12 +1,9 @@
-tests/cases/conformance/parser/ecmascript5/MemberAccessorDeclarations/parserMemberAccessorDeclaration15.ts(2,8): error TS2369: A parameter property is only allowed in a constructor implementation.
 tests/cases/conformance/parser/ecmascript5/MemberAccessorDeclarations/parserMemberAccessorDeclaration15.ts(2,12): error TS2369: A parameter property is only allowed in a constructor implementation.
 
 
-==== tests/cases/conformance/parser/ecmascript5/MemberAccessorDeclarations/parserMemberAccessorDeclaration15.ts (2 errors) ====
+==== tests/cases/conformance/parser/ecmascript5/MemberAccessorDeclarations/parserMemberAccessorDeclaration15.ts (1 errors) ====
     class C {
        set Foo(public a: number) { }
-           ~~~
-!!! error TS2369: A parameter property is only allowed in a constructor implementation.
                ~~~~~~~~~~~~~~~~
 !!! error TS2369: A parameter property is only allowed in a constructor implementation.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/readonlyInNonPropertyParameters.errors.txt b/tests/baselines/reference/readonlyInNonPropertyParameters.errors.txt
new file mode 100644
index 00000000000..696404c6d98
--- /dev/null
+++ b/tests/baselines/reference/readonlyInNonPropertyParameters.errors.txt
@@ -0,0 +1,19 @@
+tests/cases/compiler/readonlyInNonPropertyParameters.ts(4,9): error TS2369: A parameter property is only allowed in a constructor implementation.
+tests/cases/compiler/readonlyInNonPropertyParameters.ts(5,8): error TS2369: A parameter property is only allowed in a constructor implementation.
+tests/cases/compiler/readonlyInNonPropertyParameters.ts(7,2): error TS2369: A parameter property is only allowed in a constructor implementation.
+
+
+==== tests/cases/compiler/readonlyInNonPropertyParameters.ts (3 errors) ====
+    
+    // `readonly` won't work outside of property parameters
+    class X {
+    	method(readonly x: number) {}
+    	       ~~~~~~~~~~~~~~~~~~
+!!! error TS2369: A parameter property is only allowed in a constructor implementation.
+    	set x(readonly value: number) {}
+    	      ~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2369: A parameter property is only allowed in a constructor implementation.
+    }
+    (readonly x) => 0;
+     ~~~~~~~~~~
+!!! error TS2369: A parameter property is only allowed in a constructor implementation.
\ No newline at end of file
diff --git a/tests/baselines/reference/readonlyInNonPropertyParameters.js b/tests/baselines/reference/readonlyInNonPropertyParameters.js
new file mode 100644
index 00000000000..484a726dc4d
--- /dev/null
+++ b/tests/baselines/reference/readonlyInNonPropertyParameters.js
@@ -0,0 +1,23 @@
+//// [readonlyInNonPropertyParameters.ts]
+
+// `readonly` won't work outside of property parameters
+class X {
+	method(readonly x: number) {}
+	set x(readonly value: number) {}
+}
+(readonly x) => 0;
+
+//// [readonlyInNonPropertyParameters.js]
+// `readonly` won't work outside of property parameters
+var X = (function () {
+    function X() {
+    }
+    X.prototype.method = function (x) { };
+    Object.defineProperty(X.prototype, "x", {
+        set: function (value) { },
+        enumerable: true,
+        configurable: true
+    });
+    return X;
+}());
+(function (x) { return 0; });
diff --git a/tests/cases/compiler/readonlyInNonPropertyParameters.ts b/tests/cases/compiler/readonlyInNonPropertyParameters.ts
new file mode 100644
index 00000000000..7373d046e38
--- /dev/null
+++ b/tests/cases/compiler/readonlyInNonPropertyParameters.ts
@@ -0,0 +1,8 @@
+//@target: ES5
+
+// `readonly` won't work outside of property parameters
+class X {
+	method(readonly x: number) {}
+	set x(readonly value: number) {}
+}
+(readonly x) => 0;
\ No newline at end of file