diff --git a/lang/rust/avro/src/de.rs b/lang/rust/avro/src/de.rs
index 691faae2769..cf010f15bb6 100644
--- a/lang/rust/avro/src/de.rs
+++ b/lang/rust/avro/src/de.rs
@@ -653,6 +653,8 @@ mod tests {
     use serde::Serialize;
     use uuid::Uuid;
 
+    use crate::set_serde_human_readable;
+
     use super::*;
 
     #[derive(Debug, Deserialize, Serialize, Clone, PartialEq, Eq)]
@@ -1230,9 +1232,7 @@ mod tests {
         // AVRO-3747: set serde's is_human_readable to false
         use serde::de::Deserializer as SerdeDeserializer;
 
-        unsafe {
-            crate::util::SERDE_HUMAN_READABLE = false;
-        }
+        set_serde_human_readable(false);
 
         let deser = Deserializer::new(&Value::Null);
 
@@ -1246,9 +1246,7 @@ mod tests {
         // AVRO-3747: set serde's is_human_readable to true
         use serde::de::Deserializer as SerdeDeserializer;
 
-        unsafe {
-            crate::util::SERDE_HUMAN_READABLE = true;
-        }
+        set_serde_human_readable(true);
 
         let deser = Deserializer::new(&Value::Null);
 
diff --git a/lang/rust/avro/src/ser.rs b/lang/rust/avro/src/ser.rs
index 1c7718ba724..31f741de7f1 100644
--- a/lang/rust/avro/src/ser.rs
+++ b/lang/rust/avro/src/ser.rs
@@ -488,6 +488,8 @@ pub fn to_value<S: Serialize>(value: S) -> Result<Value, Error> {
 
 #[cfg(test)]
 mod tests {
+    use crate::set_serde_human_readable;
+
     use super::*;
     use pretty_assertions::assert_eq;
     use serde::{Deserialize, Serialize};
@@ -1007,9 +1009,7 @@ mod tests {
     fn avro_3747_human_readable_false() {
         use serde::ser::Serializer as SerdeSerializer;
 
-        unsafe {
-            crate::util::SERDE_HUMAN_READABLE = false;
-        }
+        set_serde_human_readable(false);
 
         let ser = &mut Serializer {};
 
@@ -1020,9 +1020,7 @@ mod tests {
     fn avro_3747_human_readable_true() {
         use serde::ser::Serializer as SerdeSerializer;
 
-        unsafe {
-            crate::util::SERDE_HUMAN_READABLE = true;
-        }
+        set_serde_human_readable(true);
 
         let ser = &mut Serializer {};
 
diff --git a/lang/rust/avro/src/util.rs b/lang/rust/avro/src/util.rs
index 695a1a6c7f0..00b2c0b35b7 100644
--- a/lang/rust/avro/src/util.rs
+++ b/lang/rust/avro/src/util.rs
@@ -17,23 +17,24 @@
 
 use crate::{schema::Documentation, AvroResult, Error};
 use serde_json::{Map, Value};
-use std::{convert::TryFrom, i64, io::Read, sync::Once};
+use std::{
+    convert::TryFrom,
+    i64,
+    io::Read,
+    sync::atomic::{AtomicBool, AtomicUsize, Ordering},
+};
 
 /// Maximum number of bytes that can be allocated when decoding
 /// Avro-encoded values. This is a protection against ill-formed
 /// data, whose length field might be interpreted as enormous.
 /// See max_allocation_bytes to change this limit.
-pub const DEFAULT_MAX_ALLOCATION_BYTES: usize = 512 * 1024 * 1024;
-static mut MAX_ALLOCATION_BYTES: usize = DEFAULT_MAX_ALLOCATION_BYTES;
-static MAX_ALLOCATION_BYTES_ONCE: Once = Once::new();
+static MAX_ALLOCATION_BYTES: AtomicUsize = AtomicUsize::new(512 * 1024 * 1024);
 
 /// Whether to set serialization & deserialization traits
 /// as `human_readable` or not.
 /// See [set_serde_human_readable] to change this value.
-pub const DEFAULT_SERDE_HUMAN_READABLE: bool = true;
 // crate visible for testing
-pub(crate) static mut SERDE_HUMAN_READABLE: bool = DEFAULT_SERDE_HUMAN_READABLE;
-static SERDE_HUMAN_READABLE_ONCE: Once = Once::new();
+pub(crate) static SERDE_HUMAN_READABLE: AtomicBool = AtomicBool::new(true);
 
 pub trait MapHelper {
     fn string(&self, key: &str) -> Option<String>;
@@ -133,23 +134,13 @@ fn decode_variable<R: Read>(reader: &mut R) -> AvroResult<u64> {
 }
 
 /// Set a new maximum number of bytes that can be allocated when decoding data.
-/// Once called, the limit cannot be changed.
-///
-/// **NOTE** This function must be called before decoding **any** data. The
-/// library leverages [`std::sync::Once`](https://doc.rust-lang.org/std/sync/struct.Once.html)
-/// to set the limit either when calling this method, or when decoding for
-/// the first time.
 pub fn max_allocation_bytes(num_bytes: usize) -> usize {
-    unsafe {
-        MAX_ALLOCATION_BYTES_ONCE.call_once(|| {
-            MAX_ALLOCATION_BYTES = num_bytes;
-        });
-        MAX_ALLOCATION_BYTES
-    }
+    MAX_ALLOCATION_BYTES.store(num_bytes, Ordering::Relaxed);
+    num_bytes
 }
 
 pub fn safe_len(len: usize) -> AvroResult<usize> {
-    let max_bytes = max_allocation_bytes(DEFAULT_MAX_ALLOCATION_BYTES);
+    let max_bytes = MAX_ALLOCATION_BYTES.load(Ordering::Relaxed);
 
     if len <= max_bytes {
         Ok(len)
@@ -163,23 +154,13 @@ pub fn safe_len(len: usize) -> AvroResult<usize> {
 
 /// Set whether serializing/deserializing is marked as human readable in serde traits.
 /// This will adjust the return value of `is_human_readable()` for both.
-/// Once called, the value cannot be changed.
-///
-/// **NOTE** This function must be called before serializing/deserializing **any** data. The
-/// library leverages [`std::sync::Once`](https://doc.rust-lang.org/std/sync/struct.Once.html)
-/// to set the limit either when calling this method, or when decoding for
-/// the first time.
 pub fn set_serde_human_readable(human_readable: bool) -> bool {
-    unsafe {
-        SERDE_HUMAN_READABLE_ONCE.call_once(|| {
-            SERDE_HUMAN_READABLE = human_readable;
-        });
-        SERDE_HUMAN_READABLE
-    }
+    SERDE_HUMAN_READABLE.store(human_readable, Ordering::Relaxed);
+    human_readable
 }
 
 pub(crate) fn is_human_readable() -> bool {
-    unsafe { SERDE_HUMAN_READABLE }
+    SERDE_HUMAN_READABLE.load(Ordering::Relaxed)
 }
 
 #[cfg(test)]