diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 5b528fa..eacb325 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -4021,6 +4021,8 @@
 VarTemplateSpecializationDecl *Sema::CompleteVarTemplateSpecializationDecl(
     VarTemplateSpecializationDecl *VarSpec, VarDecl *PatternDecl,
     const MultiLevelTemplateArgumentList &TemplateArgs) {
+  assert(PatternDecl->isThisDeclarationADefinition() &&
+         "don't have a definition to instantiate from");
 
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI =
@@ -4032,6 +4034,9 @@
   // Update the type of this variable template specialization.
   VarSpec->setType(DI->getType());
 
+  // Convert the declaration into a definition now.
+  VarSpec->setCompleteDefinition();
+
   // Instantiate the initializer.
   InstantiateVariableInitializer(VarSpec, PatternDecl, TemplateArgs);
 
@@ -4225,6 +4230,10 @@
   if (Var->isInvalidDecl())
     return;
 
+  // FIXME: We're missing ASTMutationListener notifications for all of the work
+  // done here. (Some of our callers notify the listeners for the static data
+  // member case, but not in general.)
+
   VarTemplateSpecializationDecl *VarSpec =
       dyn_cast<VarTemplateSpecializationDecl>(Var);
   VarDecl *PatternDecl = nullptr, *Def = nullptr;