Index: docs/LibFuzzer.rst
===================================================================
--- docs/LibFuzzer.rst
+++ docs/LibFuzzer.rst
@@ -68,6 +68,7 @@
   sync_timeout                       	600	Minimum timeout between syncs.
   use_traces                            0       Experimental: use instruction traces
   only_ascii                            0       If 1, generate only ASCII (isprint+isspace) inputs.
+  test_single_input                     ""      Use specified file content as test input. Test will be run only once. Useful for debugging a particular case.
 
 
 For the full list of flags run the fuzzer binary with ``-help=1``.
Index: lib/Fuzzer/FuzzerDriver.cpp
===================================================================
--- lib/Fuzzer/FuzzerDriver.cpp
+++ lib/Fuzzer/FuzzerDriver.cpp
@@ -202,6 +202,12 @@
   return 0;
 }
 
+int RunOneTest(Fuzzer *F, const char *InputFilePath) {
+  Unit U = FileToVector(InputFilePath);
+  F->ExecuteCallback(U);
+  return 0;
+}
+
 int FuzzerDriver(int argc, char **argv, UserCallback Callback) {
   FuzzerRandomLibc Rand(0);
   SimpleUserSuppliedFuzzer SUSF(&Rand, Callback);
@@ -275,6 +281,9 @@
   if (Flags.apply_tokens)
     return ApplyTokens(F, Flags.apply_tokens);
 
+  if (Flags.test_single_input)
+    return RunOneTest(&F, Flags.test_single_input);
+
   unsigned Seed = Flags.seed;
   // Initialize Seed.
   if (Seed == 0)
Index: lib/Fuzzer/FuzzerFlags.def
===================================================================
--- lib/Fuzzer/FuzzerFlags.def
+++ lib/Fuzzer/FuzzerFlags.def
@@ -66,3 +66,4 @@
                                "trace-based-mutations (tbm).")
 FUZZER_FLAG_INT(tbm_width, 5, "Apply at most this number of independent"
                                "trace-based-mutations (tbm)")
+FUZZER_FLAG_STRING(test_single_input, "Use specified file as test input.")
\ No newline at end of file
Index: lib/Fuzzer/FuzzerInternal.h
===================================================================
--- lib/Fuzzer/FuzzerInternal.h
+++ lib/Fuzzer/FuzzerInternal.h
@@ -115,10 +115,10 @@
   static void StaticAlarmCallback();
 
   Unit SubstituteTokens(const Unit &U) const;
+  void ExecuteCallback(const Unit &U);
 
  private:
   void AlarmCallback();
-  void ExecuteCallback(const Unit &U);
   void MutateAndTestOne(Unit *U);
   void ReportNewCoverage(size_t NewCoverage, const Unit &U);
   size_t RunOne(const Unit &U);
Index: lib/Fuzzer/test/fuzzer.test
===================================================================
--- lib/Fuzzer/test/fuzzer.test
+++ lib/Fuzzer/test/fuzzer.test
@@ -1,6 +1,7 @@
 CHECK: BINGO
 
 RUN: LLVMFuzzer-SimpleTest 2>&1 | FileCheck %s
+RUN: LLVMFuzzer-SimpleTest -test_single_input=%S/hi.txt 2>&1 | FileCheck %s 
 
 RUN: not LLVMFuzzer-InfiniteTest -timeout=2 2>&1 | FileCheck %s --check-prefix=InfiniteTest
 InfiniteTest: ALARM: working on the last Unit for
Index: lib/Fuzzer/test/hi.txt
===================================================================
--- /dev/null
+++ lib/Fuzzer/test/hi.txt
@@ -0,0 +1 @@
+Hi!
\ No newline at end of file