diff --git a/include/simulink_math_fcn.lusi b/include/simulink_math_fcn.lusi
index c4c1630f7fc18c8277a6211e361691987edc90e9..1f926509a1a4e38fab00bba887f19a1105f0cc36 100644
--- a/include/simulink_math_fcn.lusi
+++ b/include/simulink_math_fcn.lusi
@@ -31,6 +31,8 @@ A future version can be specialized for concrete datatypes (single, double,
 *)
 
 -- open <math>
+function fmod (x,y: real) returns (z: real) prototype C lib m;
+
 function exp_scalar_real (x: real) returns (y: real) prototype C lib m;
 function log_scalar_real (x: real) returns (y: real) prototype C lib m;
 function _10u_scalar_real (x: real) returns (y: real) prototype C lib m;