diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -276,6 +276,11 @@
   ``-mfix-cortex-a72-aes-1655431``. The pass is enabled when using either of
   these cpus with ``-mcpu=`` and can be disabled using
   ``-mno-fix-cortex-a57-aes-1742098`` or ``-mno-fix-cortex-a72-aes-1655431``.
+- Added the ``-fexperimental-max-bitint-width=`` option to increase the maximum
+  allowed bit width of ``_BitInt`` types beyond the default of 128 bits. Some
+  operations, such as division or float-to-integer conversion, on ``_BitInt``
+  types with more than 128 bits currently crash clang. This option will be
+  removed in the future once clang supports all such operations.
 
 Deprecated Compiler Flags
 -------------------------
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -445,6 +445,11 @@
 
 VALUE_LANGOPT(FuchsiaAPILevel, 32, 0, "Fuchsia API level")
 
+// This option will be removed in the future once the backend
+// supports all operations (like division or float-to-integer conversion)
+// on large _BitInts.
+BENIGN_VALUE_LANGOPT(MaxBitIntWidth, 32, 128, "Maximum width of a _BitInt")
+
 #undef LANGOPT
 #undef COMPATIBLE_LANGOPT
 #undef BENIGN_LANGOPT
diff --git a/clang/include/clang/Basic/TargetInfo.h b/clang/include/clang/Basic/TargetInfo.h
--- a/clang/include/clang/Basic/TargetInfo.h
+++ b/clang/include/clang/Basic/TargetInfo.h
@@ -31,6 +31,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Frontend/OpenMP/OMPGridValues.h"
+#include "llvm/IR/DerivedTypes.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/VersionTuple.h"
@@ -235,6 +236,8 @@
 
   unsigned MaxOpenCLWorkGroupSize;
 
+  Optional<unsigned> MaxBitIntWidth;
+
   Optional<llvm::Triple> DarwinTargetVariantTriple;
 
   // TargetInfo Constructor.  Default initializes all fields.
@@ -595,11 +598,16 @@
   // Different targets may support a different maximum width for the _BitInt
   // type, depending on what operations are supported.
   virtual size_t getMaxBitIntWidth() const {
+    // Consider -fexperimental-max-bitint-width= first.
+    if (MaxBitIntWidth)
+      return std::min<size_t>(*MaxBitIntWidth, llvm::IntegerType::MAX_INT_BITS);
+
     // FIXME: this value should be llvm::IntegerType::MAX_INT_BITS, which is
     // maximum bit width that LLVM claims its IR can support. However, most
-    // backends currently have a bug where they only support division
-    // operations on types that are <= 128 bits and crash otherwise. We're
-    // setting the max supported value to 128 to be conservative.
+    // backends currently have a bug where they only support float to int
+    // conversion (and vice versa) on types that are <= 128 bits and crash
+    // otherwise. We're setting the max supported value to 128 to be
+    // conservative.
     return 128;
   }
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -6082,6 +6082,12 @@
 def fobjc_gc : Flag<["-"], "fobjc-gc">, Group<f_Group>,
   HelpText<"Enable Objective-C garbage collection">;
 
+def fexperimental_max_bitint_width_EQ:
+  Joined<["-"], "fexperimental-max-bitint-width=">, Group<f_Group>,
+  MetaVarName<"<N>">,
+  HelpText<"Set the maximum bitwidth for _BitInt (this option is expected to be removed in the future)">,
+  MarshallingInfoInt<LangOpts<"MaxBitIntWidth">>;
+
 } // let Flags = [CC1Option, NoDriverOption]
 
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -150,6 +150,9 @@
   PlatformMinVersion = VersionTuple();
 
   MaxOpenCLWorkGroupSize = 1024;
+
+  MaxBitIntWidth.reset();
+
   ProgramAddrSpace = 0;
 }
 
@@ -478,6 +481,9 @@
     Diags.Report(diag::err_opt_not_valid_on_target) << "-fprotect-parens";
     Opts.ProtectParens = false;
   }
+
+  if (Opts.MaxBitIntWidth)
+    MaxBitIntWidth = Opts.MaxBitIntWidth;
 }
 
 bool TargetInfo::initFeatureMap(
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -314,7 +314,7 @@
 
 #define BENIGN_LANGOPT(Name, Bits, Default, Description)
 #define BENIGN_ENUM_LANGOPT(Name, Type, Bits, Default, Description)
-#define BENIGN_VALUE_LANGOPT(Name, Type, Bits, Default, Description)
+#define BENIGN_VALUE_LANGOPT(Name, Bits, Default, Description)
 #include "clang/Basic/LangOptions.def"
 
   if (ExistingLangOpts.ModuleFeatures != LangOpts.ModuleFeatures) {
diff --git a/clang/test/Sema/large-bit-int.c b/clang/test/Sema/large-bit-int.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/large-bit-int.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fexperimental-max-bitint-width=1024 -fsyntax-only -verify %s
+
+void f() {
+  _Static_assert(__BITINT_MAXWIDTH__ == 1024, "Macro value is unexpected.");
+
+  _BitInt(1024) a;
+  unsigned _BitInt(1024) b;
+
+  _BitInt(8388609) c;                // expected-error {{signed _BitInt of bit sizes greater than 1024 not supported}}
+  unsigned _BitInt(0xFFFFFFFFFF) d; // expected-error {{unsigned _BitInt of bit sizes greater than 1024 not supported}}
+}