diff --git a/.gitignore b/.gitignore
index e2e6283..7d6ed6c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
-target
-.vscode
-.idea
-*.lock
+/target
+/.vscode
+/.idea
+/*.lock
+/.zed
 # internal script
-clean
+/clean
diff --git a/Cargo.toml b/Cargo.toml
index 6592ccd..ea95e89 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,6 +12,7 @@ rust-version = "1.81.0"
 [dependencies]
 cfg-if = "1"
 fastrand = { version = "2", default-features = false }
+integer-sqrt = "0"
 num-bigint = { version = "0", default-features = false }
 rayon = { version = "1", optional = true }
 regex = { version = "1", default-features = false }
diff --git a/src/algorithm/prime.rs b/src/algorithm/prime.rs
index 050ad21..126e1be 100644
--- a/src/algorithm/prime.rs
+++ b/src/algorithm/prime.rs
@@ -4,7 +4,10 @@
 
 #[cfg(feature = "std")] use rayon::prelude::*;
 
-use {crate::num::power::modpow, fastrand::Rng, num_bigint::BigUint, snafu::Snafu};
+use {
+    crate::num::power::modpow, fastrand::Rng, integer_sqrt::IntegerSquareRoot, num_bigint::BigUint,
+    snafu::Snafu,
+};
 
 /// If number is less than 2, we can't say that number is either prime or composite.
 #[non_exhaustive]
@@ -142,8 +145,8 @@ pub fn sqrtest(num: usize) -> Result<PrimeStatus, PrimeStatusError> {
         Err(PrimeStatusError)
     } else {
         // FIXME: https://github.com/rust-lang/rust/issues/116226
-        // let sqrt_res = num.isqrt().unsigned_abs()
-        let sqrt_res = (num as f64).sqrt().ceil() as usize;
+        // let sqrt_res = num.isqrt() + 1;
+        let sqrt_res = num.integer_sqrt() + 1;
         if (3..=sqrt_res).into_par_iter().find_any(|&i| num % i == 0).is_some() {
             Ok(PrimeStatus::Composite)
         } else {