diff --git a/clang/include/clang/AST/FormatString.h b/clang/include/clang/AST/FormatString.h
--- a/clang/include/clang/AST/FormatString.h
+++ b/clang/include/clang/AST/FormatString.h
@@ -127,8 +127,12 @@
     dArg,
     DArg, // Apple extension
     iArg,
+    // C23 conversion specifiers.
+    bArg,
+    BArg,
+
     IntArgBeg = dArg,
-    IntArgEnd = iArg,
+    IntArgEnd = BArg,
 
     oArg,
     OArg, // Apple extension
diff --git a/clang/lib/AST/FormatString.cpp b/clang/lib/AST/FormatString.cpp
--- a/clang/lib/AST/FormatString.cpp
+++ b/clang/lib/AST/FormatString.cpp
@@ -624,6 +624,8 @@
 
 const char *ConversionSpecifier::toString() const {
   switch (kind) {
+  case bArg: return "b";
+  case BArg: return "B";
   case dArg: return "d";
   case DArg: return "D";
   case iArg: return "i";
@@ -753,6 +755,8 @@
     case LengthModifier::AsSizeT:
     case LengthModifier::AsPtrDiff:
       switch (CS.getKind()) {
+        case ConversionSpecifier::bArg:
+        case ConversionSpecifier::BArg:
         case ConversionSpecifier::dArg:
         case ConversionSpecifier::DArg:
         case ConversionSpecifier::iArg:
@@ -908,6 +912,8 @@
 bool FormatSpecifier::hasStandardConversionSpecifier(
     const LangOptions &LangOpt) const {
   switch (CS.getKind()) {
+    case ConversionSpecifier::bArg:
+    case ConversionSpecifier::BArg:
     case ConversionSpecifier::cArg:
     case ConversionSpecifier::dArg:
     case ConversionSpecifier::iArg:
diff --git a/clang/lib/AST/PrintfFormatString.cpp b/clang/lib/AST/PrintfFormatString.cpp
--- a/clang/lib/AST/PrintfFormatString.cpp
+++ b/clang/lib/AST/PrintfFormatString.cpp
@@ -326,6 +326,14 @@
     case 's': k = ConversionSpecifier::sArg; break;
     case 'u': k = ConversionSpecifier::uArg; break;
     case 'x': k = ConversionSpecifier::xArg; break;
+    // C23.
+    case 'b':
+      if (isFreeBSDKPrintf)
+        k = ConversionSpecifier::FreeBSDbArg; // int followed by char *
+      else
+        k = ConversionSpecifier::bArg;
+      break;
+    case 'B': k = ConversionSpecifier::BArg; break;
     // POSIX specific.
     case 'C': k = ConversionSpecifier::CArg; break;
     case 'S': k = ConversionSpecifier::SArg; break;
@@ -337,11 +345,6 @@
     case '@': k = ConversionSpecifier::ObjCObjArg; break;
     // Glibc specific.
     case 'm': k = ConversionSpecifier::PrintErrno; break;
-    // FreeBSD kernel specific.
-    case 'b':
-      if (isFreeBSDKPrintf)
-        k = ConversionSpecifier::FreeBSDbArg; // int followed by char *
-      break;
     case 'r':
       if (isFreeBSDKPrintf)
         k = ConversionSpecifier::FreeBSDrArg; // int
@@ -961,8 +964,10 @@
   if (!HasAlternativeForm)
     return true;
 
-  // Alternate form flag only valid with the oxXaAeEfFgG conversions
+  // Alternate form flag only valid with the bBoxXaAeEfFgG conversions
   switch (CS.getKind()) {
+  case ConversionSpecifier::bArg:
+  case ConversionSpecifier::BArg:
   case ConversionSpecifier::oArg:
   case ConversionSpecifier::OArg:
   case ConversionSpecifier::xArg:
@@ -988,8 +993,10 @@
   if (!HasLeadingZeroes)
     return true;
 
-  // Leading zeroes flag only valid with the diouxXaAeEfFgG conversions
+  // Leading zeroes flag only valid with the bBdiouxXaAeEfFgG conversions
   switch (CS.getKind()) {
+  case ConversionSpecifier::bArg:
+  case ConversionSpecifier::BArg:
   case ConversionSpecifier::dArg:
   case ConversionSpecifier::DArg:
   case ConversionSpecifier::iArg:
@@ -1080,8 +1087,10 @@
   if (Precision.getHowSpecified() == OptionalAmount::NotSpecified)
     return true;
 
-  // Precision is only valid with the diouxXaAeEfFgGsP conversions
+  // Precision is only valid with the bBdiouxXaAeEfFgGsP conversions
   switch (CS.getKind()) {
+  case ConversionSpecifier::bArg:
+  case ConversionSpecifier::BArg:
   case ConversionSpecifier::dArg:
   case ConversionSpecifier::DArg:
   case ConversionSpecifier::iArg:
diff --git a/clang/test/Sema/format-strings-fixit.c b/clang/test/Sema/format-strings-fixit.c
--- a/clang/test/Sema/format-strings-fixit.c
+++ b/clang/test/Sema/format-strings-fixit.c
@@ -21,6 +21,7 @@
   printf("%s", (int) 123);
   printf("abc%0f", "testing testing 123");
   printf("%u", (long) -12);
+  printf("%b", (long) -13);
   printf("%p", 123);
   printf("%c\n", "x");
   printf("%c\n", 1.23);
@@ -179,6 +180,7 @@
 // CHECK: printf("%d", (int) 123);
 // CHECK: printf("abc%s", "testing testing 123");
 // CHECK: printf("%ld", (long) -12);
+// CHECK: printf("%ld", (long) -13);
 // CHECK: printf("%d", 123);
 // CHECK: printf("%s\n", "x");
 // CHECK: printf("%f\n", 1.23);
diff --git a/clang/test/Sema/format-strings.c b/clang/test/Sema/format-strings.c
--- a/clang/test/Sema/format-strings.c
+++ b/clang/test/Sema/format-strings.c
@@ -199,7 +199,7 @@
 
 void check_invalid_specifier(FILE* fp, char *buf)
 {
-  printf("%s%lb%d","unix",10,20); // expected-warning {{invalid conversion specifier 'b'}} expected-warning {{data argument not used by format string}}
+  printf("%s%lv%d","unix",10,20); // expected-warning {{invalid conversion specifier 'v'}} expected-warning {{data argument not used by format string}}
   fprintf(fp,"%%%l"); // expected-warning {{incomplete format specifier}}
   sprintf(buf,"%%%%%ld%d%d", 1, 2, 3); // expected-warning{{format specifies type 'long' but the argument has type 'int'}}
   snprintf(buf, 2, "%%%%%ld%;%d", 1, 2, 3); // expected-warning{{format specifies type 'long' but the argument has type 'int'}} expected-warning {{invalid conversion specifier ';'}} expected-warning {{data argument not used by format string}}
@@ -304,6 +304,7 @@
   printf("%qp", (void *)0); // expected-warning{{length modifier 'q' results in undefined behavior or no effect with 'p' conversion specifier}}
   printf("hhX %hhX", (unsigned char)10); // no-warning
   printf("llX %llX", (long long) 10); // no-warning
+  printf("%llb %llB", (long long) 10, (long long) 10); // no-warning
   // This is fine, because there is an implicit conversion to an int.
   printf("%d", (unsigned char) 10); // no-warning
   printf("%d", (long long) 10); // expected-warning{{format specifies type 'int' but the argument has type 'long long'}}
@@ -429,6 +430,7 @@
   // Bad flag usage
   printf("%#p", (void *) 0); // expected-warning{{flag '#' results in undefined behavior with 'p' conversion specifier}}
   printf("%0d", -1); // no-warning
+  printf("%0b%0B", -1u, -1u); // no-warning
   printf("%-p", (void *) 0); // no-warning
 #if !defined(__ANDROID__) && !defined(__Fuchsia__)
   printf("%#n", (int *) 0); // expected-warning{{flag '#' results in undefined behavior with 'n' conversion specifier}}
@@ -499,6 +501,7 @@
 void pr8641(void) {
   printf("%#x\n", 10);
   printf("%#X\n", 10);
+  printf("%#b %#B\n", 10, 10u);
 }
 
 void posix_extensions(void) {
@@ -508,6 +511,8 @@
   printf("%'i\n", 123456789); // no-warning
   printf("%'f\n", (float) 1.0); // no-warning
   printf("%'p\n", (void*) 0); // expected-warning{{results in undefined behavior with 'p' conversion specifier}}
+  printf("%'b\n", 123456789); // expected-warning{{results in undefined behavior with 'b' conversion specifier}}
+  printf("%'B\n", 123456789); // expected-warning{{results in undefined behavior with 'B' conversion specifier}}
 }
 
 // PR8486
@@ -540,6 +545,7 @@
   printf("%hhi", x); // no-warning
   printf("%c", x); // no-warning
   printf("%hhu", y); // no-warning
+  printf("%hhb %hhB", x, x); // no-warning
 }
 
 // Test suppression of individual warnings.
diff --git a/clang/test/SemaObjC/format-strings-objc.m b/clang/test/SemaObjC/format-strings-objc.m
--- a/clang/test/SemaObjC/format-strings-objc.m
+++ b/clang/test/SemaObjC/format-strings-objc.m
@@ -56,7 +56,7 @@
 
 void check_nslog(unsigned k) {
   NSLog(@"%d%%", k); // no-warning
-  NSLog(@"%s%lb%d", "unix", 10, 20); // expected-warning {{invalid conversion specifier 'b'}} expected-warning {{data argument not used by format string}}
+  NSLog(@"%s%lv%d", "unix", 10, 20); // expected-warning {{invalid conversion specifier 'v'}} expected-warning {{data argument not used by format string}}
 }
 
 // Check type validation