diff --git a/src/expressions.cu b/src/expressions.cu
index a95b1bef..2d656ce1 100644
--- a/src/expressions.cu
+++ b/src/expressions.cu
@@ -10,7 +10,7 @@ Expr::Expr(Chainable<Tensor>* chainable) : pimpl_(chainable) {}
 Expr::Expr(Float v) : pimpl_(new ConstantNode(keywords::value=v,
                                               keywords::shape={1,1})) {}
 
-Tensor Expr::val() {
+Tensor &Expr::val() {
   return pimpl_->val();
 }
 
diff --git a/src/expressions.h b/src/expressions.h
index d7945f07..09d0edfa 100644
--- a/src/expressions.h
+++ b/src/expressions.h
@@ -15,7 +15,7 @@ class Expr {
       return *this;
     }
     
-    Tensor val();
+    Tensor &val();
     Tensor grad();
     
     void forward(size_t batchSize);
diff --git a/src/graph.h b/src/graph.h
index 15b4721d..33de8a5e 100644
--- a/src/graph.h
+++ b/src/graph.h
@@ -17,7 +17,7 @@ struct Chainable {
     virtual void allocate(size_t) = 0;
     
     virtual const Shape& shape() = 0;
-    virtual DataType val() = 0;
+    virtual DataType &val() = 0;
     virtual DataType grad() = 0;
     virtual void setVal(Tensor t) {
       UTIL_THROW2("Tensors can only be assigned to input nodes"); 
@@ -82,7 +82,7 @@ class Node : public Chainable<Tensor>,
       }
     }
     
-    virtual Tensor val()  {
+    virtual Tensor &val()  {
       UTIL_THROW_IF2(!val_, "Tensor has not been allocated");
       return val_;
     };
@@ -104,4 +104,4 @@ class Node : public Chainable<Tensor>,
     Tensor adj_;
 };
 
-}
\ No newline at end of file
+}