diff --git a/Cargo.lock b/Cargo.lock
index b52b1394..a357c4ef 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -483,12 +483,6 @@ version = "3.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2e8c087f005730276d1096a652e92a8bacee2e2472bcc9715a74d2bec38b5820"
 
-[[package]]
-name = "byte-slice-cast"
-version = "1.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "65c1bf4a04a88c54f589125563643d773f3254b5c38571395e2b591c693bbc81"
-
 [[package]]
 name = "bytemuck"
 version = "1.4.1"
@@ -1148,18 +1142,6 @@ dependencies = [
  "subtle",
 ]
 
-[[package]]
-name = "fixed-hash"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cfcf0ed7fe52a17a03854ec54a9f76d6d84508d1c0e66bc1793301c73fc8493c"
-dependencies = [
- "byteorder",
- "rand 0.8.4",
- "rustc-hex",
- "static_assertions",
-]
-
 [[package]]
 name = "flate2"
 version = "1.0.19"
@@ -1724,15 +1706,6 @@ dependencies = [
  "version_check 0.9.2",
 ]
 
-[[package]]
-name = "impl-codec"
-version = "0.5.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "df170efa359aebdd5cb7fe78edcc67107748e4737bdca8a8fb40d15ea7a877ed"
-dependencies = [
- "parity-scale-codec",
-]
-
 [[package]]
 name = "indenter"
 version = "0.3.0"
@@ -2299,18 +2272,6 @@ dependencies = [
  "group",
 ]
 
-[[package]]
-name = "parity-scale-codec"
-version = "2.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "75c823fdae1bb5ff5708ee61a62697e6296175dc671710876871c853f48592b3"
-dependencies = [
- "arrayvec 0.5.2",
- "bitvec 0.20.1",
- "byte-slice-cast",
- "serde",
-]
-
 [[package]]
 name = "parking_lot"
 version = "0.11.1"
@@ -2474,17 +2435,6 @@ dependencies = [
  "output_vt100",
 ]
 
-[[package]]
-name = "primitive-types"
-version = "0.9.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2415937401cb030a2a0a4d922483f945fa068f52a7dbb22ce0fe5f2b6f6adace"
-dependencies = [
- "fixed-hash",
- "impl-codec",
- "uint",
-]
-
 [[package]]
 name = "proc-macro-error"
 version = "1.0.4"
@@ -2958,12 +2908,6 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "08d43f7aa6b08d49f382cde6a7982047c3426db949b1424bc4b7ec9ae12c6ce2"
 
-[[package]]
-name = "rustc-hex"
-version = "2.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3e75f6a532d0fd9f7f13144f392b6ad56a32696bfcd9c78f797f16bbb6f072d6"
-
 [[package]]
 name = "rustc_version"
 version = "0.2.3"
@@ -4462,7 +4406,6 @@ dependencies = [
  "itertools 0.10.1",
  "jubjub",
  "lazy_static",
- "primitive-types",
  "proptest",
  "proptest-derive",
  "rand 0.8.4",
@@ -4478,6 +4421,7 @@ dependencies = [
  "subtle",
  "thiserror",
  "tracing",
+ "uint",
  "x25519-dalek",
  "zcash_history",
  "zebra-test",
@@ -4583,7 +4527,6 @@ dependencies = [
  "lazy_static",
  "metrics",
  "once_cell",
- "primitive-types",
  "proptest",
  "proptest-derive",
  "regex",
diff --git a/zebra-chain/Cargo.toml b/zebra-chain/Cargo.toml
index 1703a7d5..3478a2fa 100644
--- a/zebra-chain/Cargo.toml
+++ b/zebra-chain/Cargo.toml
@@ -34,7 +34,6 @@ halo2 = { git = "https://github.com/zcash/halo2.git", rev = "dda60a363001373d564
 hex = "0.4"
 jubjub = "0.6.0"
 lazy_static = "1.4.0"
-primitive-types = "0.9.0"
 rand_core = "0.6"
 ripemd160 = "0.9"
 secp256k1 = { version = "0.20.2", features = ["serde"] }
@@ -46,6 +45,7 @@ thiserror = "1"
 x25519-dalek = { version = "1.1", features = ["serde"] }
 zcash_history = { git = "https://github.com/zcash/librustzcash.git", rev = "0c3ed159985affa774e44d10172d4471d798a85a" }
 bigint = "4"
+uint = "0.9.0"
 
 proptest = { version = "0.10", optional = true }
 proptest-derive = { version = "0.3.0", optional = true }
diff --git a/zebra-chain/src/work.rs b/zebra-chain/src/work.rs
index 25b0dd49..9cefe01c 100644
--- a/zebra-chain/src/work.rs
+++ b/zebra-chain/src/work.rs
@@ -2,6 +2,7 @@
 
 pub mod difficulty;
 pub mod equihash;
+mod u256;
 
 #[cfg(any(test, feature = "proptest-impl"))]
 mod arbitrary;
diff --git a/zebra-chain/src/work/difficulty.rs b/zebra-chain/src/work/difficulty.rs
index 31bf3d9d..30c31ecc 100644
--- a/zebra-chain/src/work/difficulty.rs
+++ b/zebra-chain/src/work/difficulty.rs
@@ -23,7 +23,7 @@ use std::{
     ops::Mul,
 };
 
-use primitive_types::U256;
+pub use crate::work::u256::U256;
 
 #[cfg(any(test, feature = "proptest-impl"))]
 mod arbitrary;
diff --git a/zebra-chain/src/work/difficulty/tests/prop.rs b/zebra-chain/src/work/difficulty/tests/prop.rs
index bbc8359f..a33fb594 100644
--- a/zebra-chain/src/work/difficulty/tests/prop.rs
+++ b/zebra-chain/src/work/difficulty/tests/prop.rs
@@ -1,4 +1,3 @@
-use primitive_types::U256;
 use proptest::{arbitrary::any, prelude::*};
 
 use std::cmp::Ordering;
diff --git a/zebra-chain/src/work/u256.rs b/zebra-chain/src/work/u256.rs
new file mode 100644
index 00000000..127b56fb
--- /dev/null
+++ b/zebra-chain/src/work/u256.rs
@@ -0,0 +1,10 @@
+//! Module for a 256-bit big int structure.
+// This is a separate module to make it easier to disable clippy because
+// it raises a lot of issues in the macro.
+#![allow(clippy::all)]
+
+use uint::construct_uint;
+
+construct_uint! {
+    pub struct U256(4);
+}
diff --git a/zebra-state/Cargo.toml b/zebra-state/Cargo.toml
index 8f53542d..f1be6cb0 100644
--- a/zebra-state/Cargo.toml
+++ b/zebra-state/Cargo.toml
@@ -26,7 +26,6 @@ displaydoc = "0.2.1"
 rocksdb = "0.16.0"
 tempdir = "0.3.7"
 chrono = "0.4.19"
-primitive-types = "0.9.0"
 rlimit = "0.5.4"
 
 [dev-dependencies]
@@ -40,4 +39,3 @@ tempdir = "0.3.7"
 tokio = { version = "0.3.6", features = ["full"] }
 proptest = "0.10.1"
 proptest-derive = "0.3"
-primitive-types = "0.9.0"
diff --git a/zebra-state/src/service/check/difficulty.rs b/zebra-state/src/service/check/difficulty.rs
index c394ac98..0944add3 100644
--- a/zebra-state/src/service/check/difficulty.rs
+++ b/zebra-state/src/service/check/difficulty.rs
@@ -6,14 +6,17 @@
 //!  * `median-time-past`.
 
 use chrono::{DateTime, Duration, Utc};
-use primitive_types::U256;
 
 use std::{cmp::max, cmp::min, convert::TryInto};
 
 use zebra_chain::{
-    block, block::Block, parameters::Network, parameters::NetworkUpgrade,
-    parameters::POW_AVERAGING_WINDOW, work::difficulty::CompactDifficulty,
+    block,
+    block::Block,
+    parameters::Network,
+    parameters::NetworkUpgrade,
+    parameters::POW_AVERAGING_WINDOW,
     work::difficulty::ExpandedDifficulty,
+    work::difficulty::{CompactDifficulty, U256},
 };
 
 /// The median block span for time median calculations.
diff --git a/zebra-state/src/tests.rs b/zebra-state/src/tests.rs
index 247a80aa..2abbbe70 100644
--- a/zebra-state/src/tests.rs
+++ b/zebra-state/src/tests.rs
@@ -1,12 +1,11 @@
 use std::{convert::TryFrom, mem, sync::Arc};
 
-use primitive_types::U256;
 use zebra_chain::{
     block::{self, Block},
     transaction::Transaction,
     transparent,
     work::difficulty::ExpandedDifficulty,
-    work::difficulty::Work,
+    work::difficulty::{Work, U256},
 };
 
 use super::*;