diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index f77fca2a69e00..70149464b3a99 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -2669,8 +2669,9 @@ FormulaType SubsumptionChecker::Normalize(const NormalizedConstraint &NC) {
     });
 
     if (Compound.getCompoundKind() == FormulaType::Kind) {
+      unsigned SizeLeft = Left.size();
       Res = std::move(Left);
-      Res.reserve(Left.size() + Right.size());
+      Res.reserve(SizeLeft + Right.size());
       std::for_each(std::make_move_iterator(Right.begin()),
                     std::make_move_iterator(Right.end()), Add);
       return Res;