diff --git a/tket-qsystem/src/extension/qsystem.rs b/tket-qsystem/src/extension/qsystem.rs
index dc036fcf7..b169283e4 100644
--- a/tket-qsystem/src/extension/qsystem.rs
+++ b/tket-qsystem/src/extension/qsystem.rs
@@ -394,27 +394,25 @@ pub trait QSystemOpBuilder: Dataflow + UnwrapBuilder + ArrayOpBuilder {
 
     /// Build a CY gate in terms of QSystem primitives.
     fn build_cy(&mut self, a: Wire, b: Wire) -> Result<[Wire; 2], BuildError> {
+        let pi = pi_mul_f64(self, 1.0);
         let pi_2 = pi_mul_f64(self, 0.5);
         let pi_minus_2 = pi_mul_f64(self, -0.5);
-        let zero = pi_mul_f64(self, 0.0);
 
-        let a = self.add_phased_x(a, pi_minus_2, zero)?;
+        let a = self.add_phased_x(a, pi, pi)?;
+        let b = self.add_phased_x(b, pi_minus_2, pi)?;
         let [a, b] = self.build_zz_max(a, b)?;
-        let a = self.add_rz(a, pi_2)?;
-        let b = self.add_phased_x(b, pi_2, pi_2)?;
-        let b = self.add_rz(b, pi_minus_2)?;
+        let a = self.add_phased_x(a, pi, pi_2)?;
+        let b = self.add_phased_x(b, pi_minus_2, pi_minus_2)?;
+        let a = self.add_rz(a, pi_minus_2)?;
+        let b = self.add_rz(b, pi_2)?;
         Ok([a, b])
     }
 
     /// Build a CZ gate in terms of QSystem primitives.
     fn build_cz(&mut self, a: Wire, b: Wire) -> Result<[Wire; 2], BuildError> {
-        let pi = pi_mul_f64(self, 1.0);
         let pi_2 = pi_mul_f64(self, 0.5);
-        let pi_minus_2 = pi_mul_f64(self, -0.5);
 
-        let a = self.add_phased_x(a, pi, pi_2)?;
         let [a, b] = self.build_zz_max(a, b)?;
-        let a = self.add_phased_x(a, pi, pi_minus_2)?;
         let b = self.add_rz(b, pi_2)?;
         let a = self.add_rz(a, pi_2)?;