diff --git a/Common/Core/RecoDecay.h b/Common/Core/RecoDecay.h
index be50d7831ab..c938280e865 100644
--- a/Common/Core/RecoDecay.h
+++ b/Common/Core/RecoDecay.h
@@ -288,8 +288,8 @@ struct RecoDecay {
   static double cpaRZ(const T& posPV, const U& posSV, const std::array<V, 3>& mom)
   {
     // CPARZ = (r . pz)/(|r| |pz|)
-    auto lineDecay = std::array{sqrtSumOfSquares(posSV[0] - posPV[0], posSV[1] - posPV[1]), posSV[2] - posPV[2]};
-    auto momRZ = std::array{sqrtSumOfSquares(mom[0], mom[1]), mom[2]};
+    auto lineDecay = std::array{sqrtSumOfSquares(posSV[0] - posPV[0], posSV[1] - posPV[1]), static_cast<double>(posSV[2] - posPV[2])};
+    auto momRZ = std::array{sqrtSumOfSquares(mom[0], mom[1]), static_cast<double>(mom[2])};
     auto cos = dotProd(lineDecay, momRZ) / std::sqrt(mag2(lineDecay) * mag2(momRZ));
     if (cos < -1.) {
       return -1.;