diff --git a/generation/src/Add.hs b/generation/src/Add.hs
index 7cc9969..dc3ffe0 100644
--- a/generation/src/Add.hs
+++ b/generation/src/Add.hs
@@ -202,6 +202,7 @@ declareSafeSignedAddOperators bitsize _ =
       testFileLit = Lit [] (Str (testFile False bitsize) Cooked Unsuffixed mempty) mempty
   in [sourceFile|
         use core::ops::Add;
+        #[cfg(test)]
         use crate::CryptoNum;
         #[cfg(test)]
         use crate::testing::{build_test_path,run_test};
diff --git a/generation/src/ModInv.hs b/generation/src/ModInv.hs
index b0fdf96..2fffd76 100644
--- a/generation/src/ModInv.hs
+++ b/generation/src/ModInv.hs
@@ -36,13 +36,15 @@ declareModInv bitsize _ =
         testFileLit = Lit [] (Str (testFile True bitsize) Cooked Unsuffixed mempty) mempty
     in [sourceFile|
         use core::convert::TryFrom;
-        use crate::CryptoNum;
+        use crate::{CryptoNum,ModularInversion};
         use crate::signed::$$sname;
         #[cfg(test)]
         use crate::testing::{build_test_path,run_test};
         use crate::unsigned::$$uname;
 
-        impl $$uname {
+        impl ModularInversion for $$uname {
+            type Signed = $$sname;
+
             fn modinv(&self, phi: &$$uname) -> Option<$$uname>
             {
                 let (_, mut b, g) = phi.egcd(&self);
diff --git a/generation/src/Subtract.hs b/generation/src/Subtract.hs
index 81229fc..55f2531 100644
--- a/generation/src/Subtract.hs
+++ b/generation/src/Subtract.hs
@@ -133,6 +133,7 @@ declareSafeSignedSubtractOperators bitsize _ =
       testFileLit = Lit [] (Str (testFile True bitsize) Cooked Unsuffixed mempty) mempty
   in [sourceFile|
         use core::ops::Sub;
+        #[cfg(test)]
         use crate::CryptoNum;
         #[cfg(test)]
         use crate::testing::{build_test_path,run_test};
diff --git a/src/lib.rs b/src/lib.rs
index e535b48..a1254e5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -52,8 +52,10 @@ pub trait DivMod: Sized {
     fn divmod(&self, rhs: &Self) -> (Self, Self);
 }
 
-// Provides support for a variety of modular mathematical operations, as beloved
-// by cryptographers.
+/// Provides support for a variety of modular mathematical operations, as beloved
+/// by cryptographers. Note that modular inversion and GCD calculations are shoved
+/// off into another trait, because they operate on slightly different number
+/// types.
 pub trait ModularOperations<Modulus=Self> {
     // reduce the current value by the provided modulus
     fn reduce(&self, m: &Modulus) -> Self;
@@ -66,6 +68,18 @@ pub trait ModularOperations<Modulus=Self> {
 
 }
 
+/// Provide support for modular inversion and GCD operations, which are useful
+/// here and there. We provide default implementations for `modinv` and
+/// `gcd_is_one`, based on the implementation of `egcd`. The built-in versions
+/// explicitly define the latter, though, to improve performance.
+pub trait ModularInversion: Sized {
+    type Signed;
+
+    fn modinv(&self, phi: &Self) -> Option<Self>;
+    fn egcd(&self, rhs: &Self) -> (Self::Signed, Self::Signed, Self::Signed);
+    fn gcd_is_one(&self, b: &Self) -> bool;
+}
+
 /// An error in conversion of large numbers (either to primitives or to other numbers
 #[derive(Debug)]
 pub enum ConversionError {