diff --git a/CHANGELOG.md b/CHANGELOG.md
index 20cd863..02feb41 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,18 @@
 # Changelog
 
+## 0.2.1
+
+### Changed
+- performance improvement: internally `get_difficulty` was being called
+  multiple times while generating `PoW`, now it calls only once.
+
+## 0.2.0
+
+### Changed
+- Difficulty factor is now an unsigned 32 bit number
+
 ## 0.1
+
+### Added:
 - PoW constructor
 - unique salt
-
-## 0.2
-- Difficulty factor is now an unsigned 32 bit number
diff --git a/Cargo.lock b/Cargo.lock
index 8ece04e..f92283f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -138,7 +138,7 @@ checksum = "624a8340c38c1b80fd549087862da4ba43e08858af025b236e509b6649fc13d5"
 
 [[package]]
 name = "pow_sha256"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "bincode",
  "derive_builder",
diff --git a/Cargo.toml b/Cargo.toml
index 1b71c7d..0197f09 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "pow_sha256"
-version = "0.2.0"
+version = "0.2.1"
 authors = [ "Aravinth Manivannan <realaravinth@bastsense.net>", "Robert Kornacki <robk@syre.io>"]
 description = """
 SHA256 PoW on any serializable datatype used in mCaptcha
diff --git a/src/lib.rs b/src/lib.rs
index 6c662e2..d7256b0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -69,7 +69,8 @@ impl Config {
         let prefix_sha = Sha256::new().chain(&self.salt).chain(prefix);
         let mut n = 0;
         let mut result = 0;
-        while result < get_difficulty(difficulty) {
+        let difficulty = get_difficulty(difficulty);
+        while result < difficulty {
             n += 1;
             result = score(prefix_sha.clone(), n);
         }