diff --git a/src/lib.rs b/src/lib.rs
index 0281954..5b51db9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -208,6 +208,33 @@ pub trait Integer: Sized + Num + PartialOrd + Ord + Eq {
         (self.extended_gcd(other), self.lcm(other))
     }
 
+    /// Inverse of the number modulo the modulus
+    ///
+    /// # Examples
+    ///
+    /// ~~~
+    /// # extern crate num_integer;
+    /// # fn main() {
+    /// # use num_integer::Integer;
+    /// assert_eq!((10isize).invmod(&11isize).unwrap(), 10isize);
+    /// assert_eq!((173isize).invmod(&1729isize).unwrap(), 10isize);
+    /// # }
+    /// ~~~
+    #[inline]
+    fn invmod(&self, modulus: &Self) -> Option<Self>
+    where
+        Self: Clone,
+    {
+        let ExtendedGcd { gcd, x, .. } = self.extended_gcd(modulus);
+        if !gcd.is_one() {
+            None
+        } else if x < Self::zero() {
+            Some(x + modulus.clone())
+        } else {
+            Some(x)
+        }
+    }
+
     /// Deprecated, use `is_multiple_of` instead.
     fn divides(&self, other: &Self) -> bool;
 
@@ -1341,3 +1368,11 @@ fn test_multinomial() {
     check_multinomial!(u64, &[0], 1);
     check_multinomial!(u64, &[12345], 1);
 }
+
+#[test]
+fn test_invmod() {
+    assert_eq!((10isize).invmod(&11isize).unwrap(), 10isize);
+    assert_eq!((173isize).invmod(&1729isize).unwrap(), 10isize);
+
+    assert!((10isize).invmod(&12isize).is_none());
+}