Index: lib/Fuzzer/FuzzerDriver.cpp
===================================================================
--- lib/Fuzzer/FuzzerDriver.cpp
+++ lib/Fuzzer/FuzzerDriver.cpp
@@ -200,10 +200,10 @@
   }
 }
 
-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 @@
     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);
   }
@@ -236,14 +236,14 @@
 }
 
 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();
@@ -378,7 +378,7 @@
   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)
Index: lib/Fuzzer/FuzzerFlags.def
===================================================================
--- lib/Fuzzer/FuzzerFlags.def
+++ lib/Fuzzer/FuzzerFlags.def
@@ -51,10 +51,10 @@
                 "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,
Index: lib/Fuzzer/FuzzerLoop.cpp
===================================================================
--- lib/Fuzzer/FuzzerLoop.cpp
+++ lib/Fuzzer/FuzzerLoop.cpp
@@ -247,7 +247,7 @@
 }
 
 void Fuzzer::CrashCallback() {
-  Printf("==%d== ERROR: libFuzzer: deadly signal\n", GetPid());
+  Printf("==%lu== ERROR: libFuzzer: deadly signal\n", GetPid());
   if (EF->__sanitizer_print_stack_trace)
     EF->__sanitizer_print_stack_trace();
   Printf("NOTE: libFuzzer has rudimentary signal handlers.\n"
@@ -262,7 +262,7 @@
 }
 
 void Fuzzer::InterruptCallback() {
-  Printf("==%d== libFuzzer: run interrupted; exiting\n", GetPid());
+  Printf("==%lu== libFuzzer: run interrupted; exiting\n", GetPid());
   std::lock_guard<std::mutex> Lock(RunningCBMtx);
   if (RunningCB) // The fuzzer is in a consistent state.
     PrintFinalStats();
@@ -286,7 +286,7 @@
     Printf("       and the timeout value is %d (use -timeout=N to change)\n",
            Options.UnitTimeoutSec);
     DumpCurrentUnit("timeout-");
-    Printf("==%d== ERROR: libFuzzer: timeout after %d seconds\n", GetPid(),
+    Printf("==%lu== ERROR: libFuzzer: timeout after %d seconds\n", GetPid(),
            Seconds);
     if (EF->__sanitizer_print_stack_trace)
       EF->__sanitizer_print_stack_trace();
@@ -298,7 +298,7 @@
 
 void Fuzzer::RssLimitCallback() {
   Printf(
-      "==%d== ERROR: libFuzzer: out-of-memory (used: %zdMb; limit: %zdMb)\n",
+      "==%lu== ERROR: libFuzzer: out-of-memory (used: %zdMb; limit: %zdMb)\n",
       GetPid(), GetPeakRSSMb(), Options.RssLimitMb);
   Printf("   To change the out-of-memory limit use -rss_limit_mb=<N>\n\n");
   if (EF->__sanitizer_print_memory_profile)
Index: lib/Fuzzer/FuzzerUtil.h
===================================================================
--- lib/Fuzzer/FuzzerUtil.h
+++ lib/Fuzzer/FuzzerUtil.h
@@ -38,7 +38,7 @@
 
 std::string DescribePC(const char *SymbolizedFMT, uintptr_t PC);
 
-int NumberOfCpuCores();
+unsigned NumberOfCpuCores();
 
 // Platform specific functions.
 struct SignalHandlerOptions {
@@ -58,7 +58,7 @@
 
 void SleepSeconds(int Seconds);
 
-int GetPid();
+unsigned long GetPid();
 
 size_t GetPeakRSSMb();
 
Index: lib/Fuzzer/FuzzerUtil.cpp
===================================================================
--- lib/Fuzzer/FuzzerUtil.cpp
+++ lib/Fuzzer/FuzzerUtil.cpp
@@ -195,7 +195,7 @@
     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 "
Index: lib/Fuzzer/FuzzerUtilPosix.cpp
===================================================================
--- lib/Fuzzer/FuzzerUtilPosix.cpp
+++ lib/Fuzzer/FuzzerUtilPosix.cpp
@@ -109,7 +109,7 @@
   sleep(Seconds);  // Use C API to avoid coverage from instrumented libc++.
 }
 
-int GetPid() { return getpid(); }
+unsigned long GetPid() { return (unsigned long)getpid(); }
 
 size_t GetPeakRSSMb() {
   struct rusage usage;
Index: lib/Fuzzer/FuzzerUtilWindows.cpp
===================================================================
--- lib/Fuzzer/FuzzerUtilWindows.cpp
+++ lib/Fuzzer/FuzzerUtilWindows.cpp
@@ -139,7 +139,7 @@
   Sleep(Seconds * 1000);
 }
 
-int GetPid() { return GetCurrentProcessId(); }
+unsigned long GetPid() { return GetCurrentProcessId(); }
 
 size_t GetPeakRSSMb() {
   PROCESS_MEMORY_COUNTERS info;