Index: clang/lib/AST/ASTImporter.cpp
===================================================================
--- clang/lib/AST/ASTImporter.cpp
+++ clang/lib/AST/ASTImporter.cpp
@@ -8166,7 +8166,19 @@
           FromRecord, ToRecord, ASTNodeImporter::IDK_Basic))
         return std::move(Err);
     } else {
-      CompleteDecl(ToRecord);
+      // If FromRecord is not defined we need to force it to be.
+      // Simply calling CompleteDecl(...) for a RecordDecl will break some cases
+      // it will start the definition but we never finish it.
+      // If a RecordDecl has base classes they won't be imported and we will
+      // be missing anything that we inherit from those bases.
+      if (FromRecord->hasExternalLexicalStorage() &&
+          !FromRecord->isCompleteDefinition())
+        FromRecord->getASTContext().getExternalSource()->CompleteType(
+            FromRecord);
+
+      if (Error Err = ASTNodeImporter(*this).ImportDefinition(
+              FromRecord, ToRecord, ASTNodeImporter::IDK_Basic))
+        return std::move(Err);
     }
   } else if (auto *ToEnum = dyn_cast<EnumDecl>(ToDC)) {
     auto *FromEnum = cast<EnumDecl>(FromDC);
Index: lldb/test/API/commands/expression/import_base_class_when_class_has_derived_member/TestImportBaseClassWhenClassHasDerivedMember.py
===================================================================
--- /dev/null
+++ lldb/test/API/commands/expression/import_base_class_when_class_has_derived_member/TestImportBaseClassWhenClassHasDerivedMember.py
@@ -0,0 +1,4 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals())
Index: lldb/test/API/commands/expression/import_base_class_when_class_has_derived_member/main.cpp
===================================================================
--- /dev/null
+++ lldb/test/API/commands/expression/import_base_class_when_class_has_derived_member/main.cpp
@@ -0,0 +1,36 @@
+struct B {
+  int dump() const;
+};
+
+int B::dump() const { return 42; }
+
+// Derived class D obtains dump() method from base class B
+struct D : public B {
+  // Introduce a TypedefNameDecl
+  using Iterator = D *;
+};
+
+struct C {
+  // This will cause use to invoke VisitTypedefNameDecl(...) when Importing
+  // the DeclContext of C.
+  // We will invoke ImportContext(...) which should force the From Decl to
+  // be defined if it not already defined. We will then Import the definition
+  // to the To Decl.
+  // This will force processing of the base class of D which allows us to see
+  // base class methods such as dump().
+  D::Iterator iter;
+
+  bool f(D *DD) {
+    return true; //%self.expect_expr("DD->dump()", result_type="int",
+                 // result_value="42")
+  }
+};
+
+int main() {
+  C c;
+  D d;
+
+  c.f(&d);
+
+  return 0;
+}