diff --git a/tfhe/src/core_crypto/commons/parameters.rs b/tfhe/src/core_crypto/commons/parameters.rs
index 6e648d234b..0eeb5cac3a 100644
--- a/tfhe/src/core_crypto/commons/parameters.rs
+++ b/tfhe/src/core_crypto/commons/parameters.rs
@@ -137,8 +137,9 @@ pub struct PolynomialSize(pub usize);
 
 impl PolynomialSize {
     /// Return the associated [`PolynomialSizeLog`].
+    /// If the polynomial size is not a power of 2, returns the floor of its log2
     pub fn log2(&self) -> PolynomialSizeLog {
-        PolynomialSizeLog((self.0 as f64).log2().ceil() as usize)
+        PolynomialSizeLog(self.0.ilog2() as usize)
     }
 
     pub fn to_fourier_polynomial_size(&self) -> FourierPolynomialSize {