diff --git a/src/env.cc b/src/env.cc
index fffe5d61d0685a..76d1b6dd86d43e 100644
--- a/src/env.cc
+++ b/src/env.cc
@@ -306,7 +306,7 @@ void Environment::PrintSyncTrace() const {
   Local<v8::StackTrace> stack =
       StackTrace::CurrentStackTrace(isolate(), 10, StackTrace::kDetailed);
 
-  fprintf(stderr, "(node:%u) WARNING: Detected use of sync API\n",
+  fprintf(stderr, "(node:%d) WARNING: Detected use of sync API\n",
           uv_os_getpid());
 
   for (int i = 0; i < stack->GetFrameCount() - 1; i++) {
diff --git a/src/util.cc b/src/util.cc
index 77824acb03a610..3e808e13fe87d8 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -115,7 +115,7 @@ std::string GetHumanReadableProcessName() {
 void GetHumanReadableProcessName(char (*name)[1024]) {
   char title[1024] = "Node.js";
   uv_get_process_title(title, sizeof(title));
-  snprintf(*name, sizeof(*name), "%s[%u]", title, uv_os_getpid());
+  snprintf(*name, sizeof(*name), "%s[%d]", title, uv_os_getpid());
 }
 
 }  // namespace node