diff --git a/lib/Index/IndexBody.cpp b/lib/Index/IndexBody.cpp
index 9439c11..08d233f 100644
--- a/lib/Index/IndexBody.cpp
+++ b/lib/Index/IndexBody.cpp
@@ -165,6 +165,9 @@
     if (!TD)
       return true;
     CXXRecordDecl *RD = TD->getTemplatedDecl();
+    if (!RD->hasDefinition())
+      return true;
+    RD = RD->getDefinition();
     std::vector<const NamedDecl *> Symbols =
         RD->lookupDependentName(NameInfo.getName(), Filter);
     // FIXME: Improve overload handling.
diff --git a/lib/Index/IndexTypeSourceInfo.cpp b/lib/Index/IndexTypeSourceInfo.cpp
index 7e2041c..e9ca651 100644
--- a/lib/Index/IndexTypeSourceInfo.cpp
+++ b/lib/Index/IndexTypeSourceInfo.cpp
@@ -157,6 +157,9 @@
     if (!TD)
       return true;
     CXXRecordDecl *RD = TD->getTemplatedDecl();
+    if (!RD->hasDefinition())
+      return true;
+    RD = RD->getDefinition();
     DeclarationName Name(DNT->getIdentifier());
     std::vector<const NamedDecl *> Symbols = RD->lookupDependentName(
         Name, [](const NamedDecl *ND) { return isa<TypeDecl>(ND); });
diff --git a/test/Index/Core/index-dependent-source.cpp b/test/Index/Core/index-dependent-source.cpp
index 35f5cf4..2541079 100644
--- a/test/Index/Core/index-dependent-source.cpp
+++ b/test/Index/Core/index-dependent-source.cpp
@@ -122,3 +122,12 @@
   object.overload1(Y());
 // CHECK-NOT: [[@LINE-1]]
 }
+
+template<typename T> struct UndefinedTemplateClass;
+
+template<typename T>
+void undefinedTemplateLookup(UndefinedTemplateClass<T> &x) {
+// Shouldn't crash!
+  x.lookup;
+  typename UndefinedTemplateClass<T>::Type y;
+}