diff --git a/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp b/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp
--- a/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp
+++ b/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp
@@ -705,6 +705,7 @@
   SmallVector<ValueRange> newCaseOperands;
   SmallVector<SmallVector<Value>> argStorage;
   auto caseValues = op.getCaseValues();
+  argStorage.reserve(caseValues->size() + 1);
   auto caseDests = op.getCaseDestinations();
   bool requiresChange = false;
   for (int64_t i = 0, size = caseValues->size(); i < size; ++i) {