diff --git a/artiq/firmware/ksupport/api.rs b/artiq/firmware/ksupport/api.rs
index 00c0f23e6..6d14891a7 100644
--- a/artiq/firmware/ksupport/api.rs
+++ b/artiq/firmware/ksupport/api.rs
@@ -70,6 +70,7 @@ static mut API: &'static [(&'static str, *const ())] = &[
     api!(sqrt),
     api!(round),
     api!(floor),
+    api!(fmod),
 
     /* exceptions */
     api!(_Unwind_Resume = ::unwind::_Unwind_Resume),