diff --git a/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp b/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp
index dccb642d5f79f..48173033ecbe2 100644
--- a/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp
+++ b/flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp
@@ -154,7 +154,7 @@ class BoxprocTypeRewriter : public mlir::TypeConverter {
                                  ty.getName().str() + boxprocSuffix.str());
       if (rec.isFinalized())
         return rec;
-      auto it = convertedTypes.try_emplace(ty, rec);
+      [[maybe_unused]] auto it = convertedTypes.try_emplace(ty, rec);
       assert(it.second && "expected ty to not be in the map");
       std::vector<RecordType::TypePair> ps = ty.getLenParamList();
       std::vector<RecordType::TypePair> cs;