diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -12977,6 +12977,10 @@
     });
   }
 
+  void VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *DAE) {
+    Visit(DAE->getExpr());
+  }
+
   void VisitCXXConstructExpr(const CXXConstructExpr *CCE) {
     // This is a call, so all subexpressions are sequenced before the result.
     SequencedSubexpression Sequenced(*this);
diff --git a/clang/test/SemaCXX/warn-unsequenced.cpp b/clang/test/SemaCXX/warn-unsequenced.cpp
--- a/clang/test/SemaCXX/warn-unsequenced.cpp
+++ b/clang/test/SemaCXX/warn-unsequenced.cpp
@@ -268,6 +268,36 @@
                                           // cxx17-warning@-1 {{unsequenced modification and access to 'pf'}}
 }
 
+namespace default_arg {
+  int a;
+  void f1(int = a, int = a++); // cxx11-warning 2{{unsequenced modification and access to 'a'}}
+                               // cxx17-warning@-1 2{{unsequenced modification and access to 'a'}}
+
+  void f2(int = a++, int = a); // cxx11-warning {{unsequenced modification and access to 'a'}}
+                               // cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
+
+  void f3(int = a++, int = sizeof(a));
+
+  void test() {
+    // TODO: Consider adding a remark indicating the function call where
+    // the default argument was used.
+    int b;
+    f1();
+    f1(a);
+    f1(a,a);     // ok
+    f1(b);       // ok
+    f1(b,a++);   // ok
+
+    f2();
+    f2(a);       // ok
+    f2(a++);     // cxx11-warning {{unsequenced modification and access to 'a'}}
+                 // cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
+
+    f3();       // ok
+    f3(a++);    // ok
+  }
+}
+
 namespace PR20819 {
   struct foo { void bar(int); };
   foo get_foo(int);