diff --git a/tools/clang/lib/Analysis/UninitializedValues.cpp b/tools/clang/lib/Analysis/UninitializedValues.cpp
index dfd689bdf3..0bcccc7e6b 100644
--- a/tools/clang/lib/Analysis/UninitializedValues.cpp
+++ b/tools/clang/lib/Analysis/UninitializedValues.cpp
@@ -171,6 +171,12 @@ class CFGBlockValues {
     return declToIndex.getHLSLOutParams();
   }
   // HLSL Change End - Treat `out` parameters as uninitialized values.
+
+  // HLSL Change Begin - check the variable is in the declToIndex map
+  bool hasValueIndex(const VarDecl *vd) {
+    return declToIndex.getValueIndex(vd).hasValue();
+  }
+  // HLSL Change End - check the variable is in the declToIndex map
 };  
 } // end anonymous namespace
 
@@ -781,10 +787,23 @@ void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
   case ClassifyRefs::Ignore:
     break;
   case ClassifyRefs::Use:
-    reportUse(dr, cast<VarDecl>(dr->getDecl()));
+    // HLSL Change Begin - check the variable is in the declToIndex map
+    // before calling reportUse(). HLSL out parameters or local variables from
+    // template instantiations may not be mapped in the current DeclContext.
+    if (const VarDecl *VD = cast<VarDecl>(dr->getDecl())) {
+      if (vals.hasValueIndex(VD))
+        reportUse(dr, VD);
+    }
+    // HLSL Change End - check the variable is in the declToIndex map
     break;
   case ClassifyRefs::Init:
-    vals[cast<VarDecl>(dr->getDecl())] = Initialized;
+    // HLSL Change Begin - check the variable is in the declToIndex map
+    // before marking it Initialized.
+    if (const VarDecl *VD = cast<VarDecl>(dr->getDecl())) {
+      if (vals.hasValueIndex(VD))
+        vals[VD] = Initialized;
+    }
+    // HLSL Change End - check the variable is in the declToIndex map
     break;
   case ClassifyRefs::SelfInit:
       handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
@@ -795,8 +814,12 @@ void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
 void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
   if (BO->getOpcode() == BO_Assign) {
     FindVarResult Var = findVar(BO->getLHS());
+    // HLSL Change Begin - check the variable is in the declToIndex map
+    // before marking it Initialized.
     if (const VarDecl *VD = Var.getDecl())
-      vals[VD] = Initialized;
+      if (vals.hasValueIndex(VD))
+        vals[VD] = Initialized;
+    // HLSL Change End - check the variable is in the declToIndex map
   }
 }
 
diff --git a/tools/clang/test/DXC/template_uninitialized_values.hlsl b/tools/clang/test/DXC/template_uninitialized_values.hlsl
new file mode 100644
index 0000000000..43d334d82c
--- /dev/null
+++ b/tools/clang/test/DXC/template_uninitialized_values.hlsl
@@ -0,0 +1,63 @@
+// RUN: dxc -E main -T cs_6_6 -HV 2021 -Wno-unused-value %s | FileCheck %s
+
+// Asserts in UnitializedValues.cpp were triggered by the following code
+// examples. The cause was that HLSL out parameters or local variables from
+// template instantiations may not be present in the declToIndex map when the
+// variable's DeclContext differs from the analysis context (common in
+// template instantiations).
+// The fix was to add defensive checks so that if the variable isn't tracked
+// it is silently ignored.
+
+// CHECK: define void @main()
+
+template <typename R>
+void test(R x, out uint result) {
+    uint repro = 0;
+    result = 10;
+}
+
+[numthreads(32, 32, 1)] void main(uint2 threadId: SV_DispatchThreadID) {
+    uint x;
+    test(10, x);
+}
+
+template <typename NameType>
+void func2(out uint var1)
+{
+    uint var3;
+    uint var4;
+    uint var5;
+    uint var6;
+    uint var7;
+    uint var8;
+    uint var9;
+    uint var10;
+    uint var11;
+    uint var12;
+    uint var13;
+    uint var14;
+    uint var15;
+    uint var16;
+    uint var17;
+    uint var18;
+    uint var19;
+    uint var20;
+    uint var21;
+    uint var22;
+    uint var23;
+    uint var24;
+    uint var25;
+    uint var26;
+    uint var27;
+    uint var28;
+    uint var29;
+    uint var30;
+    uint var31;
+    var1;
+}
+
+void func1()
+{
+    uint var33;
+    func2<uint>(var33);
+}