diff --git a/CHANGELOG.md b/CHANGELOG.md
index a14095e6e..3cdf30ddc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Next release
 
+- fix(primitives): limit legacy class sizes
 - fix(block_production): dynamic block closing now adds special address with prev block hash
 - fix(rpc): call, simulate, estimate rpcs executed on top of the block, not at the start of it
 - fix(compilation): crate-level compilation
diff --git a/crates/madara/primitives/class/src/convert.rs b/crates/madara/primitives/class/src/convert.rs
index f943a48ce..c9f39ae08 100644
--- a/crates/madara/primitives/class/src/convert.rs
+++ b/crates/madara/primitives/class/src/convert.rs
@@ -6,12 +6,10 @@ use starknet_core::types::{
     },
     CompressedLegacyContractClass,
 };
-use std::io::Read;
+use std::io::{self, Read};
 
 #[derive(Debug, thiserror::Error)]
 pub enum ParseCompressedLegacyClassError {
-    #[error("I/O error: {0}")]
-    IoError(#[from] std::io::Error),
     #[error("JSON parse error: {0}")]
     JsonError(#[from] serde_json::Error),
     #[error("Unexpected legacy compiler version string")]
@@ -20,15 +18,17 @@ pub enum ParseCompressedLegacyClassError {
     ParseIntError(#[from] std::num::ParseIntError),
 }
 
+#[allow(non_upper_case_globals)]
+const MiB: u64 = 1024 * 1024;
+const CLASS_SIZE_LIMIT: u64 = 4 * MiB;
+
 /// Attempts to recover a compressed legacy program.
 pub fn parse_compressed_legacy_class(
     class: CompressedLegacyContractClass,
 ) -> Result<LegacyContractClass, ParseCompressedLegacyClassError> {
-    let mut gzip_decoder = GzDecoder::new(class.program.as_slice());
-    let mut program_json = String::new();
-    gzip_decoder.read_to_string(&mut program_json)?;
-
-    let program = serde_json::from_str::<LegacyProgram>(&program_json)?;
+    // decompress and parse as a single [`Read`] pipeline to avoid having an intermediary buffer here.
+    let program: LegacyProgram =
+        serde_json::from_reader(ReadSizeLimiter::new(GzDecoder::new(class.program.as_slice()), CLASS_SIZE_LIMIT))?;
 
     let is_pre_0_11_0 = match &program.compiler_version {
         Some(compiler_version) => {
@@ -84,3 +84,50 @@ fn parse_legacy_entrypoint(entrypoint: &LegacyContractEntryPoint, pre_0_11_0: bo
         selector: entrypoint.selector,
     }
 }
+
+
+#[derive(thiserror::Error, Debug)]
+#[error("Read input is too large")]
+struct InputTooLarge;
+
+/// [`std::io::Read`] combinator that works very much like [`std::io::Take`], but returns an error
+/// if the underlying buffer is bigger than the limit instead of just returning EOF.
+pub struct ReadSizeLimiter<R> {
+    inner: R,
+    limit: u64,
+}
+impl<R: Read> ReadSizeLimiter<R> {
+    pub fn new(inner: R, limit: u64) -> Self {
+        Self { inner, limit }
+    }
+}
+impl<R: Read> Read for ReadSizeLimiter<R> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        if self.limit == 0 {
+            // check if the inner read still has data for us
+            if self.inner.read(&mut [0])? > 0 {
+                return Err(io::Error::new(io::ErrorKind::Other, InputTooLarge));
+            }
+        }
+
+        let max = u64::min(buf.len() as u64, self.limit) as usize;
+        let n = self.inner.read(&mut buf[..max])?;
+        // can only panic if the inner Read impl returns a bogus number
+        assert!(n as u64 <= self.limit, "number of read bytes exceeds limit");
+        self.limit -= n as u64;
+        Ok(n)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn read_size_limiter() {
+        assert!(ReadSizeLimiter::new(&[0u8; 3][..], 5).read_to_end(&mut vec![]).is_ok());
+        assert!(ReadSizeLimiter::new(&[0u8; 5][..], 5).read_to_end(&mut vec![]).is_ok());
+        assert!(ReadSizeLimiter::new(&[0u8; 6][..], 5).read_to_end(&mut vec![]).is_err());
+        assert!(ReadSizeLimiter::new(&[0u8; 64][..], 5).read_to_end(&mut vec![]).is_err());
+    }
+}