diff --git a/lib/Fuzzer/FuzzerDriver.cpp b/lib/Fuzzer/FuzzerDriver.cpp
index 1ff822c6881..f4f1a4d47d1 100644
--- a/lib/Fuzzer/FuzzerDriver.cpp
+++ b/lib/Fuzzer/FuzzerDriver.cpp
@@ -200,10 +200,10 @@ static void PulseThread() {
   }
 }
 
-static void WorkerThread(const std::string &Cmd, std::atomic<int> *Counter,
-                        int NumJobs, std::atomic<bool> *HasErrors) {
+static void WorkerThread(const std::string &Cmd, std::atomic<unsigned> *Counter,
+                         unsigned NumJobs, std::atomic<bool> *HasErrors) {
   while (true) {
-    int C = (*Counter)++;
+    unsigned C = (*Counter)++;
     if (C >= NumJobs) break;
     std::string Log = "fuzz-" + std::to_string(C) + ".log";
     std::string ToRun = Cmd + " > " + Log + " 2>&1\n";
@@ -213,7 +213,7 @@ static void WorkerThread(const std::string &Cmd, std::atomic<int> *Counter,
     if (ExitCode != 0)
       *HasErrors = true;
     std::lock_guard<std::mutex> Lock(Mu);
-    Printf("================== Job %d exited with exit code %d ============\n",
+    Printf("================== Job %u exited with exit code %d ============\n",
            C, ExitCode);
     fuzzer::CopyFileToErr(Log);
   }
@@ -231,14 +231,14 @@ std::string CloneArgsWithoutX(const std::vector<std::string> &Args,
 }
 
 static int RunInMultipleProcesses(const std::vector<std::string> &Args,
-                                  int NumWorkers, int NumJobs) {
-  std::atomic<int> Counter(0);
+                                  unsigned NumWorkers, unsigned NumJobs) {
+  std::atomic<unsigned> Counter(0);
   std::atomic<bool> HasErrors(false);
   std::string Cmd = CloneArgsWithoutX(Args, "jobs", "workers");
   std::vector<std::thread> V;
   std::thread Pulse(PulseThread);
   Pulse.detach();
-  for (int i = 0; i < NumWorkers; i++)
+  for (unsigned i = 0; i < NumWorkers; i++)
     V.push_back(std::thread(WorkerThread, Cmd, &Counter, NumJobs, &HasErrors));
   for (auto &T : V)
     T.join();
@@ -379,7 +379,7 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   if (Flags.jobs > 0 && Flags.workers == 0) {
     Flags.workers = std::min(NumberOfCpuCores() / 2, Flags.jobs);
     if (Flags.workers > 1)
-      Printf("Running %d workers\n", Flags.workers);
+      Printf("Running %u workers\n", Flags.workers);
   }
 
   if (Flags.workers > 0 && Flags.jobs > 0)
diff --git a/lib/Fuzzer/FuzzerFlags.def b/lib/Fuzzer/FuzzerFlags.def
index 6a27ca30e4a..d32d6fca1ec 100644
--- a/lib/Fuzzer/FuzzerFlags.def
+++ b/lib/Fuzzer/FuzzerFlags.def
@@ -54,10 +54,10 @@ FUZZER_FLAG_INT(use_value_profile, 0,
                 "Experimental. Use value profile to guide fuzzing.")
 FUZZER_FLAG_INT(use_cmp, 1, "Use CMP traces to guide mutations")
 FUZZER_FLAG_INT(shrink, 0, "Experimental. Try to shrink corpus elements.")
-FUZZER_FLAG_INT(jobs, 0, "Number of jobs to run. If jobs >= 1 we spawn"
+FUZZER_FLAG_UNSIGNED(jobs, 0, "Number of jobs to run. If jobs >= 1 we spawn"
                           " this number of jobs in separate worker processes"
                           " with stdout/stderr redirected to fuzz-JOB.log.")
-FUZZER_FLAG_INT(workers, 0,
+FUZZER_FLAG_UNSIGNED(workers, 0,
             "Number of simultaneous worker processes to run the jobs."
             " If zero, \"min(jobs,NumberOfCpuCores()/2)\" is used.")
 FUZZER_FLAG_INT(reload, 1,
diff --git a/lib/Fuzzer/FuzzerUtil.cpp b/lib/Fuzzer/FuzzerUtil.cpp
index 18f690c6d97..f5fd3a85187 100644
--- a/lib/Fuzzer/FuzzerUtil.cpp
+++ b/lib/Fuzzer/FuzzerUtil.cpp
@@ -195,7 +195,7 @@ void PrintPC(const char *SymbolizedFMT, const char *FallbackFMT, uintptr_t PC) {
     Printf(FallbackFMT, PC);
 }
 
-int NumberOfCpuCores() {
+unsigned NumberOfCpuCores() {
   unsigned N = std::thread::hardware_concurrency();
   if (!N) {
     Printf("WARNING: std::thread::hardware_concurrency not well defined for "
diff --git a/lib/Fuzzer/FuzzerUtil.h b/lib/Fuzzer/FuzzerUtil.h
index cac93cc141b..78b7c2489b0 100644
--- a/lib/Fuzzer/FuzzerUtil.h
+++ b/lib/Fuzzer/FuzzerUtil.h
@@ -38,7 +38,7 @@ void PrintPC(const char *SymbolizedFMT, const char *FallbackFMT, uintptr_t PC);
 
 std::string DescribePC(const char *SymbolizedFMT, uintptr_t PC);
 
-int NumberOfCpuCores();
+unsigned NumberOfCpuCores();
 
 bool ExecuteCommandAndReadOutput(const std::string &Command, std::string *Out);