diff --git a/src/kernel/constraint.cpp b/src/kernel/constraint.cpp
index eb1b1034f..840f8ac8c 100644
--- a/src/kernel/constraint.cpp
+++ b/src/kernel/constraint.cpp
@@ -115,3 +115,4 @@ std::ostream & operator<<(std::ostream & out, constraint const & c) {
     return out;
 }
 }
+void print(lean::constraint const & c) { std::cout << c << "\n"; }