diff --git a/src/ExprNode.cc b/src/ExprNode.cc
index 8652ba8a0dab7b2c83f3533d553e24dad165892d..e358911243db1553cd935aae4625a2d6bdb52457 100644
--- a/src/ExprNode.cc
+++ b/src/ExprNode.cc
@@ -458,7 +458,7 @@ void
 NumConstNode::writeJsonAST(ostream &output) const
 {
   output << R"({"node_type" : "NumConstNode", "value" : )";
-  output << datatree.num_constants.get(id) << "}";
+  output << std::stof(datatree.num_constants.get(id)) << "}";
 }
 
 void