Index: lib/Fuzzer/FuzzerInterface.h
===================================================================
--- lib/Fuzzer/FuzzerInterface.h
+++ lib/Fuzzer/FuzzerInterface.h
@@ -19,6 +19,7 @@
 #ifndef LLVM_FUZZER_INTERFACE_H
 #define LLVM_FUZZER_INTERFACE_H
 
+#include "FuzzerDefs.h"
 #include <stddef.h>
 #include <stdint.h>
 
@@ -36,12 +37,14 @@
 // If provided, this function will be called by libFuzzer once at startup.
 // It may read and modify argc/argv.
 // Must return 0.
+ATTRIBUTE_INTERFACE
 int LLVMFuzzerInitialize(int *argc, char ***argv);
 
 // Optional user-provided custom mutator.
 // Mutates raw data in [Data, Data+Size) inplace.
 // Returns the new size, which is not greater than MaxSize.
 // Given the same Seed produces the same mutation.
+ATTRIBUTE_INTERFACE
 size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size, size_t MaxSize,
                                unsigned int Seed);
 
@@ -49,6 +52,7 @@
 // Combines pieces of Data1 & Data2 together into Out.
 // Returns the new size, which is not greater than MaxOutSize.
 // Should produce the same mutation given the same Seed.
+ATTRIBUTE_INTERFACE
 size_t LLVMFuzzerCustomCrossOver(const uint8_t *Data1, size_t Size1,
                                  const uint8_t *Data2, size_t Size2,
                                  uint8_t *Out, size_t MaxOutSize,
Index: lib/Fuzzer/test/BogusInitializeTest.cpp
===================================================================
--- lib/Fuzzer/test/BogusInitializeTest.cpp
+++ lib/Fuzzer/test/BogusInitializeTest.cpp
@@ -5,6 +5,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "FuzzerInterface.h"
+
 extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) {
   ***argv = 'X';
   return 0;
Index: lib/Fuzzer/test/InitializeTest.cpp
===================================================================
--- lib/Fuzzer/test/InitializeTest.cpp
+++ lib/Fuzzer/test/InitializeTest.cpp
@@ -9,6 +9,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "FuzzerInterface.h"
+
 static char *argv0;
 
 extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) {