diff --git a/stan/math/opencl/kernel_generator/load.hpp b/stan/math/opencl/kernel_generator/load.hpp
index ae0f7d1eb6d..799cdb551a0 100644
--- a/stan/math/opencl/kernel_generator/load.hpp
+++ b/stan/math/opencl/kernel_generator/load.hpp
@@ -49,7 +49,7 @@ class load_
    * Creates a deep copy of this expression.
    * @return copy of \c *this
    */
-  inline load_<T&> deep_copy() const& { return load_<T&>(a_); }
+  inline load_<T&> deep_copy() const & { return load_<T&>(a_); }
   inline load_<T> deep_copy() && { return load_<T>(std::forward<T>(a_)); }
 
   /**