diff --git a/fuzz/Cargo.toml b/fuzz/Cargo.toml
index 4b3941da..a5addd67 100644
--- a/fuzz/Cargo.toml
+++ b/fuzz/Cargo.toml
@@ -51,3 +51,7 @@ path = "fuzz_targets/deserialize_psbt.rs"
 [[bin]]
 name = "deser_net_msg"
 path = "fuzz_targets/deser_net_msg.rs"
+
+[[bin]]
+name = "uint128_fuzz"
+path = "fuzz_targets/uint128_fuzz.rs"
diff --git a/fuzz/fuzz_targets/uint128_fuzz.rs b/fuzz/fuzz_targets/uint128_fuzz.rs
new file mode 100644
index 00000000..ce00c350
--- /dev/null
+++ b/fuzz/fuzz_targets/uint128_fuzz.rs
@@ -0,0 +1,101 @@
+extern crate bitcoin;
+use std::str::FromStr;
+
+fn do_test(data: &[u8]) {
+    macro_rules! read_ints {
+        ($start: expr) => { {
+            let mut native = 0;
+            for c in data[$start..$start + 16].iter() {
+                native <<= 8;
+                native |= (*c) as u128;
+            }
+            // Note BE:
+            let uint128 = bitcoin::util::uint::Uint128::from(&[native as u64, (native >> 8*8) as u64][..]);
+            (native, uint128)
+        } }
+    }
+    macro_rules! check_eq {
+        ($native: expr, $uint: expr) => { {
+            assert_eq!(&[$native as u64, ($native >> 8*8) as u64], $uint.as_bytes());
+        } }
+    }
+
+    if data.len() != 16*2 + 1 { return; }
+    let (a_native, a) = read_ints!(0);
+
+    // Checks using only a:
+    for i in 0..128 {
+        check_eq!(a_native << i, a << i);
+        check_eq!(a_native >> i, a >> i);
+    }
+    assert_eq!(a_native as u64, a.low_u64());
+    assert_eq!(a_native as u32, a.low_u32());
+    assert_eq!(128 - a_native.leading_zeros() as usize, a.bits());
+    assert_eq!(a_native as u64, bitcoin::util::uint::Uint128::from_u64(a_native as u64).unwrap().low_u64());
+
+    // Checks with two numbers:
+    let (b_native, b) = read_ints!(16);
+
+    check_eq!(a_native.wrapping_add(b_native), a + b);
+    check_eq!(a_native.wrapping_sub(b_native), a - b);
+    if b_native != 0 {
+        check_eq!(a_native.wrapping_div(b_native), a / b);
+    }
+    check_eq!(a_native.wrapping_mul(b_native), a * b);
+    check_eq!(a_native & b_native, a & b);
+    check_eq!(a_native | b_native, a | b);
+    check_eq!(a_native ^ b_native, a ^ b);
+    check_eq!(a_native.wrapping_mul((b_native as u32) as u128), a.mul_u32(b.low_u32()));
+
+    assert_eq!(a_native > b_native, a > b);
+    assert_eq!(a_native >= b_native, a >= b);
+    assert_eq!(a_native < b_native, a < b);
+    assert_eq!(a_native <= b_native, a <= b);
+}
+
+#[cfg(feature = "afl")]
+#[macro_use] extern crate afl;
+#[cfg(feature = "afl")]
+fn main() {
+    fuzz!(|data| {
+        do_test(&data);
+    });
+}
+
+#[cfg(feature = "honggfuzz")]
+#[macro_use] extern crate honggfuzz;
+#[cfg(feature = "honggfuzz")]
+fn main() {
+    loop {
+        fuzz!(|data| {
+            do_test(data);
+        });
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
+        let mut b = 0;
+        for (idx, c) in hex.as_bytes().iter().enumerate() {
+            b <<= 4;
+            match *c {
+                b'A'...b'F' => b |= c - b'A' + 10,
+                b'a'...b'f' => b |= c - b'a' + 10,
+                b'0'...b'9' => b |= c - b'0',
+                _ => panic!("Bad hex"),
+            }
+            if (idx & 1) == 1 {
+                out.push(b);
+                b = 0;
+            }
+        }
+    }
+
+    #[test]
+    fn duplicate_crash() {
+        let mut a = Vec::new();
+        extend_vec_from_hex("100000a70000000000000000000000000000000000000000000000000000000054", &mut a);
+        super::do_test(&a);
+    }
+}