diff --git a/src/constants.rs b/src/constants.rs
index b0820d3..63648e5 100644
--- a/src/constants.rs
+++ b/src/constants.rs
@@ -149,27 +149,22 @@ mod test {
     }
 
     #[test]
-    /// Test that SQRT_M1 and MSQRT_M1 are square roots of -1
+    /// Test that SQRT_M1 is a square root of -1
     fn test_sqrt_minus_one() {
         let minus_one = FieldElement::minus_one();
         let sqrt_m1_sq = &constants::SQRT_M1 * &constants::SQRT_M1;
-        let msqrt_m1_sq = &constants::MSQRT_M1 * &constants::MSQRT_M1;
         assert_eq!(minus_one,  sqrt_m1_sq);
-        assert_eq!(minus_one, msqrt_m1_sq);
     }
 
     #[test]
     fn test_sqrt_constants_sign() {
-        let one       = FieldElement::one();
         let minus_one = FieldElement::minus_one();
         let (was_nonzero_square, invsqrt_m1) = minus_one.invsqrt();
         assert_eq!(was_nonzero_square, 1u8);
         let sign_test_sqrt  = &invsqrt_m1 * &constants::SQRT_M1;
-        let sign_test_msqrt = &invsqrt_m1 * &constants::MSQRT_M1;
         // XXX it seems we have flipped the sign relative to
         // the invsqrt function?
         assert_eq!(sign_test_sqrt, minus_one);
-        assert_eq!(sign_test_msqrt, one);
     }
 
     /// Test that d = -121665/121666
diff --git a/src/constants_32bit.rs b/src/constants_32bit.rs
index 5fdd53c..02ef4a0 100644
--- a/src/constants_32bit.rs
+++ b/src/constants_32bit.rs
@@ -45,12 +45,6 @@ pub(crate) const SQRT_M1: FieldElement32 = FieldElement32([
     -32595792,  -7943725,   9377950,   3500415,  12389472,
     -272473,   -25146209,  -2005654,    326686,  11406482, ]);
 
-/// Precomputed value of the other square root of -1 (mod p),
-/// i.e., `MSQRT_M1 = -SQRT_M1`.
-pub(crate) const MSQRT_M1: FieldElement32 = FieldElement32([
-    32595792,    7943725,  -9377950,  -3500415, -12389472,
-    272473,     25146209,   2005654,   -326686, -11406482, ]);
-
 /// In Montgomery form y² = x³+Ax²+x, Curve25519 has A=486662.
 pub(crate) const MONTGOMERY_A: FieldElement32       = FieldElement32([
     486662, 0, 0, 0, 0, 0, 0, 0, 0, 0, ]);
diff --git a/src/constants_64bit.rs b/src/constants_64bit.rs
index 249aad0..e05768e 100644
--- a/src/constants_64bit.rs
+++ b/src/constants_64bit.rs
@@ -38,10 +38,6 @@ pub(crate) const INVSQRT_A_MINUS_D: FieldElement64 = FieldElement64([
 /// Precomputed value of one of the square roots of -1 (mod p)
 pub(crate) const SQRT_M1: FieldElement64 = FieldElement64([1718705420411056, 234908883556509, 2233514472574048, 2117202627021982, 765476049583133]);
 
-/// Precomputed value of the other square root of -1 (mod p),
-/// i.e., `MSQRT_M1 = -SQRT_M1`.
-pub(crate) const MSQRT_M1: FieldElement64 = FieldElement64([533094393274173, 2016890930128738, 18285341111199, 134597186663265, 1486323764102114]);
-
 /// In Montgomery form y² = x³+Ax²+x, Curve25519 has A=486662.
 pub(crate) const MONTGOMERY_A: FieldElement64 = FieldElement64([486662, 0, 0, 0, 0]);