diff --git a/README.md b/README.md
index 3c7d782..79a8b40 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,7 @@ code between applets, making for an overall smaller binary.
 - sync
 - touch
 - true
+- truncate
 - umount
 - unlink
 - wc
diff --git a/corebox/commands/truncate/mod.rs b/corebox/commands/truncate/mod.rs
index 8758b9b..1d09801 100644
--- a/corebox/commands/truncate/mod.rs
+++ b/corebox/commands/truncate/mod.rs
@@ -1,9 +1,7 @@
-use std::fs::File;
-
 use {
     super::Cmd,
     clap::{Arg, ArgAction, ArgGroup, Command, ValueHint},
-    std::{error::Error, fmt, fs, num::ParseIntError, path::PathBuf},
+    std::{error::Error, fmt, fs::{self, File}, num::ParseIntError, path::PathBuf},
 };
 
 #[derive(Debug, Default)]
@@ -118,7 +116,7 @@ impl Cmd for Truncate {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(Debug, PartialEq)]
 enum Operator {
     Equal,
     Add,
@@ -226,7 +224,7 @@ fn parse_size(size: &str) -> Result<Size, ParseSizeError> {
                     multiplier = Some(Multiplier::Tera);
                 }
             }
-            ch if ch.is_digit(10) => {
+            ch if ch.is_ascii_digit() => {
                 if multiplier.is_some() {
                     return Err(ParseSizeError::InvalidChar);
                 } else {
@@ -254,3 +252,36 @@ fn parse_size(size: &str) -> Result<Size, ParseSizeError> {
         }),
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn parse_size_equal() {
+        let size = parse_size("10k").unwrap();
+        assert_eq!(size.num, 10240);
+        assert_eq!(size.operator, Operator::Equal);
+    }
+
+    #[test]
+    fn parse_size_add() {
+        let size = parse_size("+4M").unwrap();
+        assert_eq!(size.num, 4194304);
+        assert_eq!(size.operator, Operator::Add);
+    }
+
+    #[test]
+    fn parse_size_remove() {
+        let size = parse_size("-2G").unwrap();
+        assert_eq!(size.num, 2147483648);
+        assert_eq!(size.operator, Operator::Remove);
+    }
+
+    #[test]
+    fn parse_size_error() {
+        let size = parse_size("10.5");
+        assert!(size.is_err());
+    }
+}
+