diff --git a/compiler/src/dmd/typesem.d b/compiler/src/dmd/typesem.d
@@ -6428,6 +6428,7 @@ RootObject compileTypeMixin(TypeMixin tm, ref const Loc loc, Scope* sc)
     auto locm = adjustLocForMixin(str, loc, global.params.mixinOut);
     scope p = new Parser!ASTCodegen(locm, sc._module, str, false, global.errorSink, &global.compileEnv, doUnittests);
     p.transitionIn = global.params.v.vin;
+    p.allowPrivateThis = global.params.privateThis;
     p.nextToken();
     //printf("p.loc.linnum = %d\n", p.loc.linnum);
 

diff --git a/compiler/test/compilable/previewhelp.d b/compiler/test/compilable/previewhelp.d
@@ -17,6 +17,7 @@ Upcoming language changes listed by -preview=name:
   =in               `in` on parameters means `scope const [ref]` and accepts rvalues
   =inclusiveincontracts 'in' contracts of overridden methods must be a superset of parent contract
   =fixImmutableConv disallow unsound immutable conversions that were formerly incorrectly permitted
+  =privateThis      add `private(this)` visibility attribute, private to the class/struct/union instead of module
   =systemVariables  disable access to variables marked '@system' from @safe code
 ----
 */
diff --git a/test/fail_compilation/prot_privatethis.d b/test/fail_compilation/prot_privatethis.d
@@ -0,0 +1,63 @@
+/*
+REQUIRED_ARGS: -preview=privateThis
+TEST_OUTPUT:
+---
+fail_compilation/prot_privatethis.d(35): Error: no property `secret` for type `prot_privatethis.C.Nested`
+fail_compilation/prot_privatethis.d(56): Error: no property `secret` for type `prot_privatethis.C`
+fail_compilation/prot_privatethis.d(57): Error: no property `internalFunc` for type `prot_privatethis.C`
+fail_compilation/prot_privatethis.d(58): Error: no property `mixedInSecret` for type `prot_privatethis.C`
+fail_compilation/prot_privatethis.d(61): Error: no property `secret` for type `prot_privatethis.U`
+---
+*/
+
+mixin template MT()
+{
+    private(this) string mixedInSecret;
+    void accessSecret() { secret++; }
+}
+
+class C
+{
+    private(this) int secret;
+    mixin MT!();
+
+    struct Nested
+    {
+        private(this) int secret;
+        void setSecret(int secret) { this.secret = secret; }
+    }
+
+    Nested nested;
+
+    this(int secret)
+    {
+        this.secret = secret;
+        nested.secret = 3; // no access
+        nested.setSecret(3); // access
+        mixedInSecret = "s"; // access
+        internalFunc(); // access
+        accessSecret(); // access
+    }
+
+    private(this) void internalFunc() { }
+}
+
+static assert(__traits(getVisibility, C.secret) == "private(this)");
+
+union U
+{
+    private(this) int secret;
+    private int butNotReally;
+}
+
+void main()
+{
+    C c = new C(2);
+    assert(c.secret == 2); // no access
+    c.internalFunc(); // no access
+    c.mixedInSecret = ""; // no access
+
+    U u;
+    u.secret = 3; // no access
+    u.butNotReally = 4; // access
+}
diff --git a/test/fail_compilation/prot_privatethis_global.d b/test/fail_compilation/prot_privatethis_global.d
@@ -0,0 +1,18 @@
+/*
+REQUIRED_ARGS: -preview=privateThis
+TEST_OUTPUT:
+---
+fail_compilation/prot_privatethis_global.d(11): Error: `private(this)` cannot be used in global scope
+fail_compilation/prot_privatethis_global.d(13): Error: `private(this)` cannot be used in global scope
+fail_compilation/prot_privatethis_global.d(16): Error: `private(this)` cannot be used in global scope
+---
+*/
+
+private(this) int x;
+
+private(this): int y;
+
+private(this)
+{
+    int z;
+}
diff --git a/test/fail_compilation/prot_privatethis_preview.d b/test/fail_compilation/prot_privatethis_preview.d
@@ -0,0 +1,11 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/prot_privatethis_preview.d(10): Error: use `-preview=privateThis` to enable usage of `private(this)`
+---
+*/
+
+class C
+{
+    private(this) int x;
+}