diff --git a/Cargo.lock b/Cargo.lock
index 22c4ba5..e2afafc 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -57,6 +57,26 @@ version = "1.0.86"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b3d1d046238990b9cf5bcde22a3fb3584ee5cf65fb2765f454ed428c7a0063da"
 
+[[package]]
+name = "big-int"
+version = "7.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "31375ce97b1316b3a92644c2cbc93fa9dcfba06e4aec9a440bce23397af82fd6"
+dependencies = [
+ "big-int-proc",
+ "thiserror",
+]
+
+[[package]]
+name = "big-int-proc"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73cfa06eb56d71f2bb1874b101a50c3ba29fcf3ff7dd8de274e473929459863b"
+dependencies = [
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "clap"
 version = "4.5.4"
@@ -145,6 +165,7 @@ name = "hb"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "big-int",
  "clap",
  "glob",
  "rayon",
@@ -217,6 +238,26 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "thiserror"
+version = "1.0.63"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c0342370b38b6a11b6cc11d6a805569958d54cfa061a29969c3b5ce2ea405724"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.63"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4558b58466b9ad7ca0f102865eccc95938dca1a74a856f2b57b6629050da261"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.12"
diff --git a/Cargo.toml b/Cargo.toml
index ae95d75..4ba1b35 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2021"
 
 [dependencies]
 anyhow = "1.0.81"
+big-int = "7.0.0"
 clap = { version = "4.4.3", features = ["derive"] }
 glob = "0.3.1"
 rayon = "1.7.0"
diff --git a/src/args.rs b/src/args.rs
index 1801879..ba9d1c4 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -2,6 +2,7 @@ use clap::{Parser, ArgAction};
 use glob::Pattern;
 use rayon::ThreadPoolBuilder;
 
+use crate::fs_size::FsSize;
 use crate::unit::Unit;
 
 use std::fs::{symlink_metadata, Metadata};
@@ -70,6 +71,14 @@ pub struct Args {
     )]
     si: bool,
 
+    #[arg(
+        short, long,
+        help = "use heap-allocated integers",
+        long_help = "use heap-allocated integers that won't overflow. Reduces performance",
+        default_value_t = false,
+    )]
+    big_int: bool,
+
     #[arg(
         short, long,
         help = "unit to print in",
@@ -159,11 +168,11 @@ impl Args {
         self
     }
 
-    pub fn len(&self, meta: &Metadata) -> u64 {
+    pub fn len<N: FsSize>(&self, meta: &Metadata) -> N {
         match self.unit {
             Unit::Blocks => meta.blocks(),
             _ => meta.len(),
-        }
+        }.into()
     }
 
     pub fn should_exclude(&self, path: &Path, file: &Metadata) -> bool {
@@ -212,6 +221,10 @@ impl Args {
     pub fn paths(&self) -> Iter<'_, String> {
         self.paths.iter()
     }
+    
+    pub fn big_int(&self) -> bool {
+        self.big_int
+    }
 }
 
 fn validate_path(s: &str) -> Result<String, String> {
diff --git a/src/directory.rs b/src/directory.rs
index bd3d9c3..0878082 100644
--- a/src/directory.rs
+++ b/src/directory.rs
@@ -5,20 +5,24 @@ use std::io::ErrorKind;
 use anyhow::{Context, Result};
 
 use crate::args::Args;
+use crate::fs_size::FsSize;
 use crate::unit::Unit;
 
 use rayon::prelude::*;
 
 #[derive(Debug, Clone)]
-pub struct Directory {
+pub struct Directory<N> {
     name: PathBuf,
-    size: u64,
-    children: Vec<Directory>,
+    size: N,
+    children: Vec<Directory<N>>,
 }
-impl Directory {
+impl<N> Directory<N>
+where
+    N: FsSize
+{
     #[inline]
-    pub const fn size(&self) -> u64 {
-        self.size
+    pub const fn size(&self) -> &N {
+        &self.size
     }
 
     pub fn new< P: AsRef<Path> >(path: P, args: &Args) -> Result<Option<Self>> {
@@ -74,13 +78,13 @@ impl Directory {
             }
         };
 
-        let fold_op = |(mut size, mut children), dir| -> Result<(u64, Vec<Self>)> {
+        let fold_op = |(mut size, mut children), dir| -> Result<(N, Vec<Self>)> {
             let dir: Self = match (dir, args.persistant()) {
                 (Ok(Some(d)), _) => d,
                 (Ok(None), _) | (Err(_), true) => return Ok((size, children)),
                 (Err(e), false) => return Err(e),
             };
-            size += dir.size;
+            size += dir.size.clone();
             if args.tree() && args.should_print(&dir.name) {
                 // since size was increased, this just prevents
                 // the directory from appearing in printing
@@ -89,10 +93,11 @@ impl Directory {
 
             Ok((size, children))
         };
-        let reduce_op = |(asize, mut avec): (u64, Vec<Self>), (bsize, bvec)| {
+        let reduce_op = |(mut asize, mut avec): (N, Vec<Self>), (bsize, bvec)| {
             if args.tree() { avec.extend(bvec); }
+            asize += bsize;
 
-            Ok((asize + bsize, avec))
+            Ok((asize, avec))
         };
 
         // this is a compicated iterator pattern. I'll do my best to explain.
@@ -106,10 +111,10 @@ impl Directory {
         .map(|entry| Self::new(entry?.path(), args))
         // 4. the fold (this is try_fold because we're iterating over Result.).
         //    each fold adds a directory as a child and increases the total size
-        .try_fold(|| (0, Vec::new()), fold_op)
+        .try_fold(|| (N::zero(), Vec::new()), fold_op)
         // 5. the final step is to reduce, which is as simple as concatenating
         //    every vector and summing up their sizes.
-        .try_reduce(|| (0, Vec::new()), reduce_op) {
+        .try_reduce(|| (N::zero(), Vec::new()), reduce_op) {
             // remember that this is a match statement?
             Ok(tuple) => tuple,
             Err(_) if args.persistant() => return Ok(None),
@@ -140,7 +145,7 @@ impl Directory {
     pub fn tree(self, unit: Unit) -> String {
         // since self.size is definitionally the greatest value, the tab length
         // is just the length of self.len, plus two for a tab width
-        let tab_size = unit.convert_with_units(self.size).len() + 2;
+        let tab_size = unit.convert_with_units(&self.size).len() + 2;
         self.vectorise(unit)
             .iter()
             .map(|e| e.stringify_tabbed(tab_size))
@@ -149,7 +154,7 @@ impl Directory {
     }
 
     /// TODO: maybe write directly to stdout to not use so much mem
-    fn vectorise(&self, unit: Unit) -> Vec<TreeEntry> {
+    fn vectorise(self, unit: Unit) -> Vec<TreeEntry<N>> {
         let mut result = Vec::new();
 
         result.push(TreeEntry::new(
@@ -168,7 +173,7 @@ impl Directory {
         // `wait` part. the last element of each one should however
         // be introduced with a `last` part, and padding should with
         // `blank`
-        for (idx, child) in self.children.iter().enumerate() {
+        for (idx, child) in self.children.into_iter().enumerate() {
             if idx+1 == len {
                 new_entry_part = TreePart::Last;
                 continue_part = TreePart::Blank;
@@ -191,21 +196,27 @@ impl Directory {
 }
 
 #[derive(Debug)]
-struct TreeEntry {
+struct TreeEntry<N> {
     parts: Vec<TreePart>,
     path: String,
-    size: u64,
+    size: N,
     unit: Unit
 }
-impl TreeEntry {
-    fn new(path: String, size: u64, unit: Unit) -> Self {
+impl<N> TreeEntry<N>
+where
+    N: FsSize
+{
+    fn new(path: String, size: N, unit: Unit) -> Self {
         Self {
             parts: Vec::new(), path, size, unit
         }
     }
 
     fn stringify_tabbed(&self, tab_size: usize) -> String {
-        let mut result = format!("{:<tab_size$}", self.unit.convert_with_units(self.size));
+        let mut result = format!(
+            "{:<tab_size$}",
+            self.unit.convert_with_units(&self.size)
+        );
 
         for part in self.parts.iter().rev() {
             result += part.display();
diff --git a/src/fs_size.rs b/src/fs_size.rs
new file mode 100644
index 0000000..50be21c
--- /dev/null
+++ b/src/fs_size.rs
@@ -0,0 +1,42 @@
+use std::fmt::Display;
+use std::ops::AddAssign;
+
+use big_int::{prelude::*, BigInt};
+
+pub trait FsSize
+    // must be convertable from u64s
+    // for getting info from Metadata::len()
+    // or Metadata::blocks()
+    : From<u64>
+    // used in the fold and reduce steps
+    + AddAssign
+    // must be printable
+    + Display
+    // rayon
+    + Send + Sync
+    + Clone
+{
+    fn zero() -> Self;
+
+    fn divide(self, rhs: u64) -> Self;
+}
+
+impl FsSize for Tight<10> {
+    fn zero() -> Self {
+        <Self as BigInt<10>>::zero()
+    }
+
+    fn divide(self, rhs: u64) -> Self {
+        self/Self::from(rhs)
+    }
+}
+
+impl FsSize for u64 {
+    fn zero() -> Self {
+        0
+    }
+
+    fn divide(self, rhs: u64) -> Self {
+        self/rhs
+    }
+}
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 3ce53e7..036855b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,20 +3,35 @@
 mod args;
 mod directory;
 mod unit;
+mod fs_size;
 
+use big_int::tight::Tight;
 use clap::Parser;
 
 use args::Args;
 use directory::Directory;
+use fs_size::FsSize;
 
 use std::process::ExitCode;
 
 fn main() -> ExitCode {
     let args = Args::parse().post_process();
 
-    let mut total = 0;
+    if args.big_int() {
+        parse_paths::<Tight<10>>(args)
+    } else {
+        parse_paths::<u64>(args)
+    }
+}
+
+fn parse_paths<N>(args: Args) -> ExitCode
+where
+    N: FsSize
+{
+    let mut total = N::zero();
+
     for path in args.paths() {
-        let dir_structure = match Directory::new(path, &args) {
+        let dir_structure = match Directory::<N>::new(path, &args) {
             Ok(Some(ds)) => ds,
             // this only ever returns None when persistant,
             // so we don't need a match guard
@@ -29,7 +44,7 @@ fn main() -> ExitCode {
             }
         };
 
-        total += dir_structure.size();
+        total += dir_structure.size().clone();
 
         if args.minimal() {
             // skip printing (this is a matter of indentation)
@@ -48,11 +63,11 @@ fn main() -> ExitCode {
     }
 
     if args.total() {
-        let total = args.unit().convert_with_units(total);
+        let total = args.unit().convert_with_units(&total);
         println!("total: {total}");
     }
     else if args.minimal() {
-        let total = args.unit().convert(total);
+        let total = args.unit().convert(&total);
         print!("{total}");
     }
 
diff --git a/src/unit.rs b/src/unit.rs
index 7a839dc..ee6ecf6 100644
--- a/src/unit.rs
+++ b/src/unit.rs
@@ -1,5 +1,7 @@
 use std::fmt::Display;
 
+use crate::fs_size::FsSize;
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Unit {
     Byte,
@@ -38,12 +40,13 @@ impl Unit {
         }
     }
 
-    pub fn convert(self, n: u64) -> String {
-        format!("{}", n/self.integer_value())
+    pub fn convert(self, n: &impl FsSize) -> String {
+        format!("{}", n.clone().divide(self.integer_value()))
     }
-    
-    pub fn convert_with_units(self, n: u64) -> String {
+
+    pub fn convert_with_units(self, n: &impl FsSize) -> String {
         self.convert(n) + self.units_pretty()
+        // todo!()
     }
 
     /// Units to print for each different unit.