diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -240,7 +240,7 @@
   "and incompatible with C++17">, InGroup<DeprecatedRegister>;
 def ext_register_storage_class : ExtWarn<
   "ISO C++17 does not allow 'register' storage class specifier">,
-  DefaultError, InGroup<Register>;
+  InGroup<Register>;
 
 def err_invalid_decl_spec_combination : Error<
   "cannot combine with previous '%0' declaration specifier">;
diff --git a/clang/test/SemaCXX/deprecated.cpp b/clang/test/SemaCXX/deprecated.cpp
--- a/clang/test/SemaCXX/deprecated.cpp
+++ b/clang/test/SemaCXX/deprecated.cpp
@@ -27,13 +27,13 @@
 
 void stuff(register int q) {
 #if __cplusplus > 201402L
-  // expected-error@-2 {{ISO C++17 does not allow 'register' storage class specifier}}
+  // expected-warning@-2 {{ISO C++17 does not allow 'register' storage class specifier}}
 #elif __cplusplus >= 201103L && !defined(NO_DEPRECATED_FLAGS)
   // expected-warning@-4 {{'register' storage class specifier is deprecated}}
 #endif
   register int n;
 #if __cplusplus > 201402L
-  // expected-error@-2 {{ISO C++17 does not allow 'register' storage class specifier}}
+  // expected-warning@-2 {{ISO C++17 does not allow 'register' storage class specifier}}
 #elif __cplusplus >= 201103L && !defined(NO_DEPRECATED_FLAGS)
   // expected-warning@-4 {{'register' storage class specifier is deprecated}}
 #endif