diff --git a/compiler-rt/lib/fuzzer/FuzzerBuiltins.h b/compiler-rt/lib/fuzzer/FuzzerBuiltins.h
--- a/compiler-rt/lib/fuzzer/FuzzerBuiltins.h
+++ b/compiler-rt/lib/fuzzer/FuzzerBuiltins.h
@@ -11,7 +11,7 @@
 #ifndef LLVM_FUZZER_BUILTINS_H
 #define LLVM_FUZZER_BUILTINS_H
 
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 
 #if !LIBFUZZER_MSVC
 #include <cstdint>
diff --git a/compiler-rt/lib/fuzzer/FuzzerBuiltinsMsvc.h b/compiler-rt/lib/fuzzer/FuzzerBuiltinsMsvc.h
--- a/compiler-rt/lib/fuzzer/FuzzerBuiltinsMsvc.h
+++ b/compiler-rt/lib/fuzzer/FuzzerBuiltinsMsvc.h
@@ -12,7 +12,7 @@
 #ifndef LLVM_FUZZER_BUILTINS_MSVC_H
 #define LLVM_FUZZER_BUILTINS_MSVC_H
 
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 
 #if LIBFUZZER_MSVC
 #include <intrin.h>
diff --git a/compiler-rt/lib/fuzzer/FuzzerDefs.h b/compiler-rt/lib/fuzzer/FuzzerDefs.h
--- a/compiler-rt/lib/fuzzer/FuzzerDefs.h
+++ b/compiler-rt/lib/fuzzer/FuzzerDefs.h
@@ -21,156 +21,6 @@
 #include <vector>
 
 
-// Platform detection.
-#ifdef __linux__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 1
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __APPLE__
-#define LIBFUZZER_APPLE 1
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __NetBSD__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 1
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __FreeBSD__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 1
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __OpenBSD__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 1
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif _WIN32
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 1
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __Fuchsia__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 1
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __EMSCRIPTEN__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 1
-#else
-#error "Support for your platform has not been implemented"
-#endif
-
-#if defined(_MSC_VER) && !defined(__clang__)
-// MSVC compiler is being used.
-#define LIBFUZZER_MSVC 1
-#else
-#define LIBFUZZER_MSVC 0
-#endif
-
-#ifndef __has_attribute
-#  define __has_attribute(x) 0
-#endif
-
-#define LIBFUZZER_POSIX                                                        \
-  (LIBFUZZER_APPLE || LIBFUZZER_LINUX || LIBFUZZER_NETBSD ||                   \
-   LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN)
-
-#ifdef __x86_64
-#  if __has_attribute(target)
-#    define ATTRIBUTE_TARGET_POPCNT __attribute__((target("popcnt")))
-#  else
-#    define ATTRIBUTE_TARGET_POPCNT
-#  endif
-#else
-#  define ATTRIBUTE_TARGET_POPCNT
-#endif
-
-
-#ifdef __clang__  // avoid gcc warning.
-#  if __has_attribute(no_sanitize)
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  endif
-#  define ALWAYS_INLINE __attribute__((always_inline))
-#else
-#  define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  define ALWAYS_INLINE
-#endif // __clang__
-
-#if LIBFUZZER_WINDOWS
-#define ATTRIBUTE_NO_SANITIZE_ADDRESS
-#else
-#define ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
-#endif
-
-#if LIBFUZZER_WINDOWS
-#define ATTRIBUTE_ALIGNED(X) __declspec(align(X))
-#define ATTRIBUTE_INTERFACE __declspec(dllexport)
-// This is used for __sancov_lowest_stack which is needed for
-// -fsanitize-coverage=stack-depth. That feature is not yet available on
-// Windows, so make the symbol static to avoid linking errors.
-#define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC static
-#define ATTRIBUTE_NOINLINE __declspec(noinline)
-#else
-#define ATTRIBUTE_ALIGNED(X) __attribute__((aligned(X)))
-#define ATTRIBUTE_INTERFACE __attribute__((visibility("default")))
-#define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC \
-  ATTRIBUTE_INTERFACE __attribute__((tls_model("initial-exec"))) thread_local
-
-#define ATTRIBUTE_NOINLINE __attribute__((noinline))
-#endif
-
-#if defined(__has_feature)
-#  if __has_feature(address_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS
-#  elif __has_feature(memory_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_MEMORY
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_ALL
-#  endif
-#else
-#  define ATTRIBUTE_NO_SANITIZE_ALL
-#endif
-
 namespace fuzzer {
 
 template <class T> T Min(T a, T b) { return a < b ? a : b; }
diff --git a/compiler-rt/lib/fuzzer/FuzzerDriver.cpp b/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
@@ -16,6 +16,7 @@
 #include "FuzzerInternal.h"
 #include "FuzzerMerge.h"
 #include "FuzzerMutate.h"
+#include "FuzzerPlatform.h"
 #include "FuzzerRandom.h"
 #include "FuzzerTracePC.h"
 #include <algorithm>
diff --git a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsDlsym.cpp b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
@@ -10,7 +10,7 @@
 // requires that clients of LibFuzzer pass ``--export-dynamic`` to the linker.
 // That is a complication we don't wish to expose to clients right now.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_APPLE
 
 #include "FuzzerExtFunctions.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp
@@ -11,7 +11,7 @@
 // weak symbols to be undefined. That is a complication we don't want to expose
 // to clients right now.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_FUCHSIA ||                \
     LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN
 
diff --git a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWindows.cpp b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWindows.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWindows.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWindows.cpp
@@ -9,7 +9,7 @@
 // compiled with MSVC. Uses weak aliases when compiled with clang. Unfortunately
 // the method each compiler supports is not supported by the other.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_WINDOWS
 
 #include "FuzzerExtFunctions.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp b/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp
@@ -8,7 +8,8 @@
 // Extra coverage counters defined by user code.
 //===----------------------------------------------------------------------===//
 
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
+#include <cstdint>
 
 #if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_FREEBSD ||                \
     LIBFUZZER_OPENBSD || LIBFUZZER_FUCHSIA || LIBFUZZER_EMSCRIPTEN
diff --git a/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp b/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 // IO functions implementation using Posix API.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_POSIX || LIBFUZZER_FUCHSIA
 
 #include "FuzzerExtFunctions.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp b/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 // IO functions implementation for Windows.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_WINDOWS
 
 #include "FuzzerExtFunctions.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerMain.cpp b/compiler-rt/lib/fuzzer/FuzzerMain.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerMain.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerMain.cpp
@@ -9,6 +9,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 
 extern "C" {
 // This function should be defined by the user.
diff --git a/compiler-rt/lib/fuzzer/FuzzerDefs.h b/compiler-rt/lib/fuzzer/FuzzerPlatform.h
copy from compiler-rt/lib/fuzzer/FuzzerDefs.h
copy to compiler-rt/lib/fuzzer/FuzzerPlatform.h
--- a/compiler-rt/lib/fuzzer/FuzzerDefs.h
+++ b/compiler-rt/lib/fuzzer/FuzzerPlatform.h
@@ -1,25 +1,15 @@
-//===- FuzzerDefs.h - Internal header for the Fuzzer ------------*- C++ -* ===//
+//===-- FuzzerPlatform.h --------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// Basic definitions.
+// Common platform macros.
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_FUZZER_DEFS_H
-#define LLVM_FUZZER_DEFS_H
-
-#include <cassert>
-#include <cstddef>
-#include <cstdint>
-#include <cstring>
-#include <memory>
-#include <set>
-#include <string>
-#include <vector>
-
+#ifndef LLVM_FUZZER_PLATFORM_H
+#define LLVM_FUZZER_PLATFORM_H
 
 // Platform detection.
 #ifdef __linux__
@@ -106,7 +96,7 @@
 #endif
 
 #ifndef __has_attribute
-#  define __has_attribute(x) 0
+#define __has_attribute(x) 0
 #endif
 
 #define LIBFUZZER_POSIX                                                        \
@@ -114,26 +104,25 @@
    LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN)
 
 #ifdef __x86_64
-#  if __has_attribute(target)
-#    define ATTRIBUTE_TARGET_POPCNT __attribute__((target("popcnt")))
-#  else
-#    define ATTRIBUTE_TARGET_POPCNT
-#  endif
+#if __has_attribute(target)
+#define ATTRIBUTE_TARGET_POPCNT __attribute__((target("popcnt")))
 #else
-#  define ATTRIBUTE_TARGET_POPCNT
+#define ATTRIBUTE_TARGET_POPCNT
+#endif
+#else
+#define ATTRIBUTE_TARGET_POPCNT
 #endif
 
-
-#ifdef __clang__  // avoid gcc warning.
-#  if __has_attribute(no_sanitize)
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  endif
-#  define ALWAYS_INLINE __attribute__((always_inline))
+#ifdef __clang__ // avoid gcc warning.
+#if __has_attribute(no_sanitize)
+#define ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
+#else
+#define ATTRIBUTE_NO_SANITIZE_MEMORY
+#endif
+#define ALWAYS_INLINE __attribute__((always_inline))
 #else
-#  define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  define ALWAYS_INLINE
+#define ATTRIBUTE_NO_SANITIZE_MEMORY
+#define ALWAYS_INLINE
 #endif // __clang__
 
 #if LIBFUZZER_WINDOWS
@@ -153,73 +142,22 @@
 #else
 #define ATTRIBUTE_ALIGNED(X) __attribute__((aligned(X)))
 #define ATTRIBUTE_INTERFACE __attribute__((visibility("default")))
-#define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC \
+#define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC                                  \
   ATTRIBUTE_INTERFACE __attribute__((tls_model("initial-exec"))) thread_local
 
 #define ATTRIBUTE_NOINLINE __attribute__((noinline))
 #endif
 
 #if defined(__has_feature)
-#  if __has_feature(address_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS
-#  elif __has_feature(memory_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_MEMORY
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_ALL
-#  endif
+#if __has_feature(address_sanitizer)
+#define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS
+#elif __has_feature(memory_sanitizer)
+#define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_MEMORY
 #else
-#  define ATTRIBUTE_NO_SANITIZE_ALL
+#define ATTRIBUTE_NO_SANITIZE_ALL
+#endif
+#else
+#define ATTRIBUTE_NO_SANITIZE_ALL
 #endif
 
-namespace fuzzer {
-
-template <class T> T Min(T a, T b) { return a < b ? a : b; }
-template <class T> T Max(T a, T b) { return a > b ? a : b; }
-
-class Random;
-class Dictionary;
-class DictionaryEntry;
-class MutationDispatcher;
-struct FuzzingOptions;
-class InputCorpus;
-struct InputInfo;
-struct ExternalFunctions;
-
-// Global interface to functions that may or may not be available.
-extern ExternalFunctions *EF;
-
-// We are using a custom allocator to give a different symbol name to STL
-// containers in order to avoid ODR violations.
-template<typename T>
-  class fuzzer_allocator: public std::allocator<T> {
-    public:
-      fuzzer_allocator() = default;
-
-      template<class U>
-      fuzzer_allocator(const fuzzer_allocator<U>&) {}
-
-      template<class Other>
-      struct rebind { typedef fuzzer_allocator<Other> other;  };
-  };
-
-template<typename T>
-using Vector = std::vector<T, fuzzer_allocator<T>>;
-
-template<typename T>
-using Set = std::set<T, std::less<T>, fuzzer_allocator<T>>;
-
-typedef Vector<uint8_t> Unit;
-typedef Vector<Unit> UnitVector;
-typedef int (*UserCallback)(const uint8_t *Data, size_t Size);
-
-int FuzzerDriver(int *argc, char ***argv, UserCallback Callback);
-
-uint8_t *ExtraCountersBegin();
-uint8_t *ExtraCountersEnd();
-void ClearExtraCounters();
-
-extern bool RunningUserCallback;
-
-}  // namespace fuzzer
-
-#endif  // LLVM_FUZZER_DEFS_H
+#endif // LLVM_FUZZER_PLATFORM_H
diff --git a/compiler-rt/lib/fuzzer/FuzzerTracePC.cpp b/compiler-rt/lib/fuzzer/FuzzerTracePC.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerTracePC.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerTracePC.cpp
@@ -19,6 +19,7 @@
 #include "FuzzerDictionary.h"
 #include "FuzzerExtFunctions.h"
 #include "FuzzerIO.h"
+#include "FuzzerPlatform.h"
 #include "FuzzerUtil.h"
 #include "FuzzerValueBitMap.h"
 #include <set>
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 // Misc utils for Darwin.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_APPLE
 #include "FuzzerCommand.h"
 #include "FuzzerIO.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 // Misc utils implementation using Fuchsia/Zircon APIs.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 
 #if LIBFUZZER_FUCHSIA
 
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 // Misc utils for Linux.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_FREEBSD ||                \
     LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN
 #include "FuzzerCommand.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 // Misc utils implementation using Posix API.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_POSIX
 #include "FuzzerIO.h"
 #include "FuzzerInternal.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 // Misc utils implementation for Windows.
 //===----------------------------------------------------------------------===//
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
 #if LIBFUZZER_WINDOWS
 #include "FuzzerCommand.h"
 #include "FuzzerIO.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerValueBitMap.h b/compiler-rt/lib/fuzzer/FuzzerValueBitMap.h
--- a/compiler-rt/lib/fuzzer/FuzzerValueBitMap.h
+++ b/compiler-rt/lib/fuzzer/FuzzerValueBitMap.h
@@ -11,7 +11,8 @@
 #ifndef LLVM_FUZZER_VALUE_BIT_MAP_H
 #define LLVM_FUZZER_VALUE_BIT_MAP_H
 
-#include "FuzzerDefs.h"
+#include "FuzzerPlatform.h"
+#include <cstdint>
 
 namespace fuzzer {