Index: clang-tools-extra/trunk/clang-tidy/bugprone/ArgumentCommentCheck.cpp
===================================================================
--- clang-tools-extra/trunk/clang-tidy/bugprone/ArgumentCommentCheck.cpp
+++ clang-tools-extra/trunk/clang-tidy/bugprone/ArgumentCommentCheck.cpp
@@ -337,7 +337,7 @@
                   llvm::makeArrayRef(Call->getArgs(), Call->getNumArgs()));
   } else {
     const auto *Construct = cast<CXXConstructExpr>(E);
-    if (Construct->getNumArgs() == 1 &&
+    if (Construct->getNumArgs() > 0 &&
         Construct->getArg(0)->getSourceRange() == Construct->getSourceRange()) {
       // Ignore implicit construction.
       return;
Index: clang-tools-extra/trunk/test/clang-tidy/bugprone-argument-comment.cpp
===================================================================
--- clang-tools-extra/trunk/test/clang-tidy/bugprone-argument-comment.cpp
+++ clang-tools-extra/trunk/test/clang-tidy/bugprone-argument-comment.cpp
@@ -63,6 +63,28 @@
   f3(/*With_Underscores=*/false);
 }
 
+namespace IgnoresImplicit {
+struct S {
+  S(int x);
+  int x;
+};
+
+struct T {
+  // Use two arguments (one defaulted) because simplistic check for implicit
+  // constructor looks for only one argument. We need to default the argument so
+  // that it will still be triggered implicitly.  This is not contrived -- it
+  // comes up in real code, for example std::set(std::initializer_list...).
+  T(S s, int y = 0);
+};
+
+void k(T arg1);
+
+void mynewtest() {
+  int foo = 3;
+  k(/*arg1=*/S(foo));
+}
+} // namespace IgnoresImplicit
+
 namespace ThisEditDistanceAboveThreshold {
 void f4(int xxx);
 void g() { f4(/*xyz=*/0); }