diff --git a/src/io.rs b/src/io.rs
index 6b6a343..f72783a 100644
--- a/src/io.rs
+++ b/src/io.rs
@@ -9,6 +9,7 @@ use std::cell::RefCell;
 
 lazy_static! {
     static ref ENTRIES: RwLock<LinkedHashMap<String, String>> = RwLock::new(LinkedHashMap::new());
+    static ref BUFFER_SIZE: usize = env::var("BIN_BUFFER_SIZE").map(|f| f.parse::<usize>().unwrap()).unwrap_or(1000usize);
 }
 
 /// Ensures `ENTRIES` is less than the size of `BIN_BUFFER_SIZE`. If it isn't then
@@ -17,10 +18,9 @@ lazy_static! {
 /// During the purge, `ENTRIES` is locked and the current thread will block.
 fn purge_old() {
     let entries_len = ENTRIES.read().unwrap().len();
-    let buffer_size = env::var("BIN_BUFFER_SIZE").map(|f| f.parse::<usize>().unwrap()).unwrap_or(1000usize);
 
-    if entries_len > buffer_size {
-        let to_remove = entries_len - buffer_size;
+    if entries_len > *BUFFER_SIZE {
+        let to_remove = entries_len - *BUFFER_SIZE;
 
         let mut entries = ENTRIES.write().unwrap();