Index: llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp
===================================================================
--- llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp
+++ llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp
@@ -238,7 +238,11 @@
 }
 
 void Fuzzer::ExecuteCallback(const Unit &U) {
-  int Res = USF.TargetFunction(U.data(), U.size());
+  const uint8_t *Data = U.data();
+  uint8_t EmptyData;
+  if (!Data) 
+    Data = &EmptyData;
+  int Res = USF.TargetFunction(Data, U.size());
   (void)Res;
   assert(Res == 0);
 }
Index: llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp
===================================================================
--- llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp
+++ llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp
@@ -1,4 +1,5 @@
 // Simple test for a fuzzer. The fuzzer must find the string "Hi!".
+#include <assert.h>
 #include <cstdint>
 #include <cstdlib>
 #include <cstddef>
@@ -7,6 +8,7 @@
 static volatile int Sink;
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  assert(Data);
   if (Size > 0 && Data[0] == 'H') {
     Sink = 1;
     if (Size > 1 && Data[1] == 'i') {