diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -69,6 +69,9 @@
 - We now generate a diagnostic for signed integer overflow due to unary minus
   in a non-constant expression context. This fixes
   `Issue 31643 <https://github.com/llvm/llvm-project/issues/31643>`_
+- Clang now warns by default for C++20 and later about deprecated capture of
+  ``this`` with a capture default of ``=``. This warning can be disabled with
+  ``-Wno-deprecated-this-capture``.
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7906,7 +7906,7 @@
     "is a C++20 extension">, InGroup<CXX20>;
   def warn_deprecated_this_capture : Warning<
     "implicit capture of 'this' with a capture default of '=' is deprecated">,
-    InGroup<DeprecatedThisCapture>, DefaultIgnore;
+    InGroup<DeprecatedThisCapture>;
   def note_deprecated_this_capture : Note<
     "add an explicit capture of 'this' to capture '*this' by reference">;
 
diff --git a/clang/test/SemaCXX/cxx1y-generic-lambdas-capturing.cpp b/clang/test/SemaCXX/cxx1y-generic-lambdas-capturing.cpp
--- a/clang/test/SemaCXX/cxx1y-generic-lambdas-capturing.cpp
+++ b/clang/test/SemaCXX/cxx1y-generic-lambdas-capturing.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -emit-llvm-only %s
-// RUN: %clang_cc1 -std=c++2a -verify -verify=expected-cxx2a -fsyntax-only -fblocks -emit-llvm-only %s
+// RUN: %clang_cc1 -std=c++2a -verify -verify=expected-cxx2a -fsyntax-only -fblocks -emit-llvm-only -Wno-deprecated-this-capture %s
 // RUN: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -emit-llvm-only -triple i386-windows-pc %s
-// RUN: %clang_cc1 -std=c++2a -verify -verify=expected-cxx2a -fsyntax-only -fblocks -emit-llvm-only -triple i386-windows-pc %s
+// RUN: %clang_cc1 -std=c++2a -verify -verify=expected-cxx2a -fsyntax-only -fblocks -emit-llvm-only -triple i386-windows-pc -Wno-deprecated-this-capture %s
 // DONTRUNYET: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -fdelayed-template-parsing %s -DDELAYED_TEMPLATE_PARSING
 // DONTRUNYET: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -fms-extensions %s -DMS_EXTENSIONS
 // DONTRUNYET: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -fdelayed-template-parsing -fms-extensions %s -DMS_EXTENSIONS -DDELAYED_TEMPLATE_PARSING
diff --git a/clang/test/SemaCXX/cxx2a-lambda-equals-this.cpp b/clang/test/SemaCXX/cxx2a-lambda-equals-this.cpp
--- a/clang/test/SemaCXX/cxx2a-lambda-equals-this.cpp
+++ b/clang/test/SemaCXX/cxx2a-lambda-equals-this.cpp
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 -std=c++2a -verify %s -Wdeprecated
+// RUN: %clang_cc1 -std=c++2a -verify %s
+// expected-no-diagnostics
 
 // This test does two things.
 // Deleting the copy constructor ensures that an [=, this] capture doesn't copy the object.
@@ -12,12 +13,3 @@
     L();
   }
 };
-
-struct B {
-  int i;
-  void f() {
-    (void) [=] { // expected-note {{add an explicit capture of 'this'}}
-      return i; // expected-warning {{implicit capture of 'this' with a capture default of '=' is deprecated}}
-    };
-  }
-};
diff --git a/clang/test/SemaCXX/lambda-implicit-this-capture.cpp b/clang/test/SemaCXX/lambda-implicit-this-capture.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/lambda-implicit-this-capture.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -std=c++11 -verify=cxx11 %s
+// RUN: %clang_cc1 -std=c++2a -verify=cxx2a %s
+// RUN: %clang_cc1 -std=c++2a -verify=cxx2a-no-deprecated %s -Wno-deprecated
+// cxx11-no-diagnostics
+// cxx2a-no-deprecated-no-diagnostics
+
+struct A {
+  int i;
+  void f() {
+    (void) [=] { // cxx2a-note {{add an explicit capture of 'this'}}
+      return i; // cxx2a-warning {{implicit capture of 'this' with a capture default of '=' is deprecated}}
+    };
+  }
+};