diff --git a/src/node.cc b/src/node.cc
index 6b6bacf5faa8f2..17963d0b11b297 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -945,7 +945,8 @@ void Init(int* argc,
   }
 
   if (per_process::cli_options->print_v8_help) {
-    V8::SetFlagsFromString("--help", 6);  // Doesn't return.
+    // Doesn't return.
+    V8::SetFlagsFromString("--help", static_cast<size_t>(6));
     UNREACHABLE();
   }
 
@@ -1002,7 +1003,8 @@ InitializationResult InitializeOncePerProcess(int argc, char** argv) {
   }
 
   if (per_process::cli_options->print_v8_help) {
-    V8::SetFlagsFromString("--help", 6);  // Doesn't return.
+    // Doesn't return.
+    V8::SetFlagsFromString("--help", static_cast<size_t>(6));
     UNREACHABLE();
   }
 
diff --git a/src/node_v8.cc b/src/node_v8.cc
index 9644468c4f6315..ed2e71de1069bb 100644
--- a/src/node_v8.cc
+++ b/src/node_v8.cc
@@ -139,7 +139,7 @@ void UpdateHeapCodeStatisticsArrayBuffer(
 void SetFlagsFromString(const FunctionCallbackInfo<Value>& args) {
   CHECK(args[0]->IsString());
   String::Utf8Value flags(args.GetIsolate(), args[0]);
-  V8::SetFlagsFromString(*flags, flags.length());
+  V8::SetFlagsFromString(*flags, static_cast<size_t>(flags.length()));
 }