diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -175,6 +175,8 @@
   SmallVector<const CXXRecordDecl*, 8> WorkList = {StartRD};
   while (!WorkList.empty()) {
     const CXXRecordDecl *RD = WorkList.pop_back_val();
+    if (RD->isDependentType())
+      continue;
     for (const CXXBaseSpecifier &BaseSpec : RD->bases()) {
       if (const CXXRecordDecl *B = BaseSpec.getType()->getAsCXXRecordDecl()) {
         if (!SeenBaseTypes.insert(B).second)
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -2648,6 +2648,9 @@
   if (auto Rec = Type->getAs<RecordType>()) {
     auto Decl = Rec->getAsCXXRecordDecl();
 
+    if (Decl->isDependentType())
+      return;
+
     // Iterate over its bases.
     for (const auto &BaseSpec : Decl->bases()) {
       QualType Base = Context.getCanonicalType(BaseSpec.getType())
diff --git a/clang/test/SemaCXX/class.cpp b/clang/test/SemaCXX/class.cpp
--- a/clang/test/SemaCXX/class.cpp
+++ b/clang/test/SemaCXX/class.cpp
@@ -211,3 +211,30 @@
 struct PR9989 { 
   static int const PR9989_Member = sizeof PR9989_Member; 
 };
+
+namespace dependent_base_type {
+struct B1 {};
+
+template <class T>
+struct S0 {
+  void m0() {
+    struct B0; // expected-note {{member is declared here}}
+
+    struct D : B0, B1 { // expected-error {{implicit instantiation}} expected-note {{in instantiation of}}
+    };
+  }
+};
+
+void test() {
+  S0<int>().m0(); // expected-note {{in instantiation of}}
+}
+
+// clang used to crash compiling this code.
+struct A {};
+template <typename T>
+struct X {
+  struct B : A {};
+  struct C : A, B {};
+};
+
+} // namespace dependent_base_type