Index: clang-tools-extra/trunk/clang-tidy/cppcoreguidelines/ProTypeMemberInitCheck.cpp
===================================================================
--- clang-tools-extra/trunk/clang-tidy/cppcoreguidelines/ProTypeMemberInitCheck.cpp
+++ clang-tools-extra/trunk/clang-tidy/cppcoreguidelines/ProTypeMemberInitCheck.cpp
@@ -449,6 +449,9 @@
 
   // Remove any bases that were explicitly written in the initializer list.
   if (Ctor) {
+    if (Ctor->isImplicit())
+      return;
+
     for (const CXXCtorInitializer *Init : Ctor->inits()) {
       if (Init->isBaseInitializer() && Init->isWritten())
         BasesToInit.erase(Init->getBaseClass()->getAsCXXRecordDecl());
Index: clang-tools-extra/trunk/test/clang-tidy/cppcoreguidelines-pro-type-member-init.cpp
===================================================================
--- clang-tools-extra/trunk/test/clang-tidy/cppcoreguidelines-pro-type-member-init.cpp
+++ clang-tools-extra/trunk/test/clang-tidy/cppcoreguidelines-pro-type-member-init.cpp
@@ -473,3 +473,16 @@
   unsigned F : 5;
   unsigned G : 5;
 };
+
+struct NegativeImplicitInheritedCtorBase {
+  NegativeImplicitInheritedCtorBase(unsigned F) : F(F) {}
+  unsigned F;
+};
+
+struct NegativeImplicitInheritedCtor : NegativeImplicitInheritedCtorBase {
+  using NegativeImplicitInheritedCtorBase::NegativeImplicitInheritedCtorBase;
+};
+
+void Bug33557() {
+  NegativeImplicitInheritedCtor I(5);
+}