diff --git a/src/shrpx_exec.cc b/src/shrpx_exec.cc
index a93ba3fb..09864dd8 100644
--- a/src/shrpx_exec.cc
+++ b/src/shrpx_exec.cc
@@ -76,14 +76,16 @@ int exec_read_command(Process &proc, char *const argv[]) {
   auto pid = fork();
 
   if (pid == 0) {
+    // This is multithreaded program, and we are allowed to use only
+    // async-signal-safe functions here.
+
     // child process
     shrpx_signal_unset_worker_proc_ign_handler();
 
     rv = shrpx_signal_unblock_all();
     if (rv != 0) {
-      auto error = errno;
-      LOG(FATAL) << "Unblocking all signals failed: errno=" << error;
-
+      constexpr char msg[] = "Unblocking all signals failed\n";
+      write(STDERR_FILENO, msg, str_size(msg));
       nghttp2_Exit(EXIT_FAILURE);
     }
 
@@ -92,9 +94,8 @@ int exec_read_command(Process &proc, char *const argv[]) {
 
     rv = execv(argv[0], argv);
     if (rv == -1) {
-      auto error = errno;
-      LOG(ERROR) << "Could not execute command: " << argv[0]
-                 << ", execve() faild, errno=" << error;
+      constexpr char msg[] = "Could not execute command\n";
+      write(STDERR_FILENO, msg, str_size(msg));
       nghttp2_Exit(EXIT_FAILURE);
     }
     // unreachable
diff --git a/src/shrpx_signal.cc b/src/shrpx_signal.cc
index fcce2dcc..5e16bf3c 100644
--- a/src/shrpx_signal.cc
+++ b/src/shrpx_signal.cc
@@ -94,7 +94,7 @@ int shrpx_signal_set(sigset_t *set) {
 
 namespace {
 template <typename Signals>
-void signal_set_handler(void (*handler)(int), Signals &&sigs) {
+int signal_set_handler(void (*handler)(int), Signals &&sigs) {
   struct sigaction act {};
   act.sa_handler = handler;
   sigemptyset(&act.sa_mask);
@@ -102,11 +102,10 @@ void signal_set_handler(void (*handler)(int), Signals &&sigs) {
   for (auto sig : sigs) {
     rv = sigaction(sig, &act, nullptr);
     if (rv != 0) {
-      auto error = errno;
-      LOG(WARN) << "sigaction() with signal " << sig
-                << " failed: errno=" << error;
+      return -1;
     }
   }
+  return 0;
 }
 } // namespace
 
@@ -120,20 +119,20 @@ constexpr auto worker_proc_ign_signals =
                         GRACEFUL_SHUTDOWN_SIGNAL, RELOAD_SIGNAL, SIGPIPE}};
 } // namespace
 
-void shrpx_signal_set_master_proc_ign_handler() {
-  signal_set_handler(SIG_IGN, master_proc_ign_signals);
+int shrpx_signal_set_master_proc_ign_handler() {
+  return signal_set_handler(SIG_IGN, master_proc_ign_signals);
 }
 
-void shrpx_signal_unset_master_proc_ign_handler() {
-  signal_set_handler(SIG_DFL, master_proc_ign_signals);
+int shrpx_signal_unset_master_proc_ign_handler() {
+  return signal_set_handler(SIG_DFL, master_proc_ign_signals);
 }
 
-void shrpx_signal_set_worker_proc_ign_handler() {
-  signal_set_handler(SIG_IGN, worker_proc_ign_signals);
+int shrpx_signal_set_worker_proc_ign_handler() {
+  return signal_set_handler(SIG_IGN, worker_proc_ign_signals);
 }
 
-void shrpx_signal_unset_worker_proc_ign_handler() {
-  signal_set_handler(SIG_DFL, worker_proc_ign_signals);
+int shrpx_signal_unset_worker_proc_ign_handler() {
+  return signal_set_handler(SIG_DFL, worker_proc_ign_signals);
 }
 
 } // namespace shrpx
diff --git a/src/shrpx_signal.h b/src/shrpx_signal.h
index c1c61b3c..8f668aef 100644
--- a/src/shrpx_signal.h
+++ b/src/shrpx_signal.h
@@ -49,11 +49,11 @@ int shrpx_signal_unblock_all();
 // -1.  The errno will indicate the error.
 int shrpx_signal_set(sigset_t *set);
 
-void shrpx_signal_set_master_proc_ign_handler();
-void shrpx_signal_unset_master_proc_ign_handler();
+int shrpx_signal_set_master_proc_ign_handler();
+int shrpx_signal_unset_master_proc_ign_handler();
 
-void shrpx_signal_set_worker_proc_ign_handler();
-void shrpx_signal_unset_worker_proc_ign_handler();
+int shrpx_signal_set_worker_proc_ign_handler();
+int shrpx_signal_unset_worker_proc_ign_handler();
 
 } // namespace shrpx