diff --git a/tools/clang/unittests/HLSLExec/LongVectorTestData.h b/tools/clang/unittests/HLSLExec/LongVectorTestData.h
index 5d668a6646..4621ad1605 100644
--- a/tools/clang/unittests/HLSLExec/LongVectorTestData.h
+++ b/tools/clang/unittests/HLSLExec/LongVectorTestData.h
@@ -184,10 +184,6 @@ struct HLSLHalf_t {
     return FromHALF((DirectX::PackedVector::XMConvertFloatToHalf(A + B)));
   }
 
-  HLSLHalf_t &operator+=(const HLSLHalf_t &Other) {
-    return *this = *this + Other;
-  }
-
   HLSLHalf_t operator-(const HLSLHalf_t &Other) const {
     const float A = DirectX::PackedVector::XMConvertHalfToFloat(Val);
     const float B = DirectX::PackedVector::XMConvertHalfToFloat(Other.Val);
diff --git a/tools/clang/unittests/HLSLExec/LongVectors.cpp b/tools/clang/unittests/HLSLExec/LongVectors.cpp
index 6d9005a9b2..af36b4782b 100644
--- a/tools/clang/unittests/HLSLExec/LongVectors.cpp
+++ b/tools/clang/unittests/HLSLExec/LongVectors.cpp
@@ -1048,10 +1048,14 @@ template <typename T> struct ExpectedBuilder<OpType::Dot, T> {
                                       const InputSets<T> &Inputs,
                                       uint16_t ScalarInputFlags) {
     UNREFERENCED_PARAMETER(ScalarInputFlags);
-    T DotProduct = T();
+
+    // Accumulate in fp32 to improve precision.
+    float DotProduct = 0.0f;
 
     for (size_t I = 0; I < Inputs[0].size(); ++I) {
-      DotProduct += Inputs[0][I] * Inputs[1][I];
+      const float A = Inputs[0][I];
+      const float B = Inputs[1][I];
+      DotProduct += A * B;
     }
 
     std::vector<T> Expected;