Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -101,8 +101,9 @@
 - ``-Wformat`` now recognizes ``%b`` for the ``printf``/``scanf`` family of
   functions and ``%B`` for the ``printf`` family of functions. Fixes
   `Issue 56885: <https://github.com/llvm/llvm-project/issues/56885>`_.
-- ``-Wbitfield-constant-conversion`` now diagnoses implicit truncation when 1 is
-  assigned to a 1-bit signed integer bitfield. This fixes
+- Introduced ``-Wsingle-bit-bitfield-constant-conversion``, grouped under
+  ``-Wbitfield-constant-conversion``, which diagnoses implicit truncation when
+  ``1`` is assigned to a 1-bit signed integer bitfield. This fixes
   `Issue 53253 <https://github.com/llvm/llvm-project/issues/53253>`_.
 - ``-Wincompatible-function-pointer-types`` now defaults to an error in all C
   language modes. It may be downgraded to a warning with
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -47,7 +47,10 @@
                                                  CXXPre14CompatBinaryLiteral,
                                                  GNUBinaryLiteral]>;
 def GNUCompoundLiteralInitializer : DiagGroup<"gnu-compound-literal-initializer">;
-def BitFieldConstantConversion : DiagGroup<"bitfield-constant-conversion">;
+def SingleBitBitFieldConstantConversion :
+  DiagGroup<"single-bit-bitfield-constant-conversion">;
+def BitFieldConstantConversion : DiagGroup<"bitfield-constant-conversion",
+                                           [SingleBitBitFieldConstantConversion]>;
 def BitFieldEnumConversion : DiagGroup<"bitfield-enum-conversion">;
 def BitFieldWidth : DiagGroup<"bitfield-width">;
 def CompoundTokenSplitByMacro : DiagGroup<"compound-token-split-by-macro">;
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3846,6 +3846,9 @@
 def warn_impcast_integer_precision_constant : Warning<
   "implicit conversion from %2 to %3 changes value from %0 to %1">,
   InGroup<ConstantConversion>;
+def warn_impcast_single_bit_bitield_precision_constant : Warning<
+  "implicit truncation from %2 to a one-bit wide bit-field changes value from "
+  "%0 to %1">, InGroup<SingleBitBitFieldConstantConversion>;
 def warn_impcast_bitfield_precision_constant : Warning<
   "implicit truncation from %2 to bit-field changes value from %0 to %1">,
   InGroup<BitFieldConstantConversion>;
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -13067,9 +13067,12 @@
   std::string PrettyValue = toString(Value, 10);
   std::string PrettyTrunc = toString(TruncatedValue, 10);
 
-  S.Diag(InitLoc, diag::warn_impcast_bitfield_precision_constant)
-    << PrettyValue << PrettyTrunc << OriginalInit->getType()
-    << Init->getSourceRange();
+  bool IsOneBit = FieldWidth == 1 && Value == 1;
+  S.Diag(InitLoc, IsOneBit
+                      ? diag::warn_impcast_single_bit_bitield_precision_constant
+                      : diag::warn_impcast_bitfield_precision_constant)
+      << PrettyValue << PrettyTrunc << OriginalInit->getType()
+      << Init->getSourceRange();
 
   return true;
 }
Index: clang/test/CXX/drs/dr6xx.cpp
===================================================================
--- clang/test/CXX/drs/dr6xx.cpp
+++ clang/test/CXX/drs/dr6xx.cpp
@@ -911,9 +911,9 @@
 namespace dr675 { // dr675: dup 739
   template<typename T> struct A { T n : 1; };
 #if __cplusplus >= 201103L
-  static_assert(A<char>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
-  static_assert(A<int>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
-  static_assert(A<long long>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
+  static_assert(A<char>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
+  static_assert(A<int>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
+  static_assert(A<long long>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
 #endif
 }
 
Index: clang/test/Sema/constant-conversion.c
===================================================================
--- clang/test/Sema/constant-conversion.c
+++ clang/test/Sema/constant-conversion.c
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -triple x86_64-apple-darwin %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,one-bit -triple x86_64-apple-darwin %s
+// RUN: %clang_cc1 -fsyntax-only -Wno-single-bit-bitfield-constant-conversion -verify -triple x86_64-apple-darwin %s
 
 // This file tests -Wconstant-conversion, a subcategory of -Wconversion
 // which is on by default.
@@ -23,7 +24,7 @@
   s.b = -2; // expected-warning {{implicit truncation from 'int' to bit-field changes value from -2 to 0}}
   s.b = -1; // no-warning
   s.b = 0;  // no-warning
-  s.b = 1;  // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
+  s.b = 1;  // one-bit-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
   s.b = 2;  // expected-warning {{implicit truncation from 'int' to bit-field changes value from 2 to 0}}
 }