Index: clang-tidy/modernize/UseNullptrCheck.cpp
===================================================================
--- clang-tidy/modernize/UseNullptrCheck.cpp
+++ clang-tidy/modernize/UseNullptrCheck.cpp
@@ -190,8 +190,10 @@
   bool VisitStmt(Stmt *S) {
     auto *C = dyn_cast<CastExpr>(S);
     // Catch the castExpr inside cxxDefaultArgExpr.
-    if (auto *E = dyn_cast<CXXDefaultArgExpr>(S))
+    if (auto *E = dyn_cast<CXXDefaultArgExpr>(S)) {
       C = dyn_cast<CastExpr>(E->getExpr());
+      FirstSubExpr = nullptr;
+    }
     if (!C) {
       FirstSubExpr = nullptr;
       return true;
Index: test/clang-tidy/modernize-use-nullptr.cpp
===================================================================
--- test/clang-tidy/modernize-use-nullptr.cpp
+++ test/clang-tidy/modernize-use-nullptr.cpp
@@ -228,3 +228,19 @@
 void test_default_argument() {
   D(nullptr);
 }
+
+// Test on two neighbour CXXDefaultArgExprs nodes.
+typedef unsigned long long uint64;
+struct ZZ {
+  explicit ZZ(uint64, const uint64* = NULL) {}
+// CHECK-MESSAGES: :[[@LINE-1]]:39: warning: use nullptr
+// CHECK-FIXES: explicit ZZ(uint64, const uint64* = nullptr) {}
+  operator bool()  { return true; }
+};
+
+uint64 Hash(uint64 seed = 0) { return 0; }
+
+void f() {
+  bool a;
+  a = ZZ(Hash());
+}