diff --git a/include/math.lusi b/include/math.lusi
index e320e6e48511c83683a16f497fbfa61f63e7c084..ffbdd2aeea07a21655b0fc36d5bf5f94415627fe 100644
--- a/include/math.lusi
+++ b/include/math.lusi
@@ -16,4 +16,3 @@ function pow (x:real; n: real) returns (y: real) prototype C lib m;
 function sin (x: real) returns (y: real) prototype C lib m;
 function sinh (x: real) returns (y: real) prototype C lib m;
 function sqrt (x: real) returns (y: real) prototype C lib m;
-function tan (x: real) returns (y: real) prototype C lib m;