diff --git a/kalk/src/prelude/mod.rs b/kalk/src/prelude/mod.rs
index 509603d..d9bb63c 100644
--- a/kalk/src/prelude/mod.rs
+++ b/kalk/src/prelude/mod.rs
@@ -516,6 +516,8 @@ pub mod funcs {
         if x.has_imaginary() || y.has_imaginary() {
             if x.imaginary_value.fract() != 0 || y.imaginary_value.fract() != 0 {
                 // Not a Gaussian integer!
+                // TODO: throw an actual error instead of returning NaN
+                return KalkNum::from(NaNf64);
             }
 
             // TODO