diff --git a/src/config.rs b/src/config.rs
index 983c670b..0d5793f1 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -69,6 +69,13 @@ pub struct Config {
     pub subgraph_service: Address,
     /// x402 payment support configuration
     pub x402: Option<X402Config>,
+    /// Maximum response size from indexers in bytes (default: 50MB)
+    #[serde(default = "default_max_indexer_response_size")]
+    pub max_indexer_response_size: usize,
+}
+
+fn default_max_indexer_response_size() -> usize {
+    50 * 1024 * 1024 // 50 MB
 }
 
 /// API keys configuration.
diff --git a/src/indexer_client.rs b/src/indexer_client.rs
index a5712ddc..715e936f 100644
--- a/src/indexer_client.rs
+++ b/src/indexer_client.rs
@@ -1,4 +1,7 @@
-use http::{StatusCode, header::CONTENT_TYPE};
+use http::{
+    StatusCode,
+    header::{CONTENT_LENGTH, CONTENT_TYPE},
+};
 use reqwest::header::AUTHORIZATION;
 use serde::{Deserialize, Serialize};
 use thegraph_core::{
@@ -31,6 +34,9 @@ pub struct IndexerResponse {
 #[derive(Clone)]
 pub struct IndexerClient {
     pub client: reqwest::Client,
+    /// Maximum allowed response size from indexers.
+    /// Prevents memory exhaustion from malicious or buggy indexers.
+    pub max_response_size: usize,
 }
 
 pub enum IndexerAuth<'a> {
@@ -79,6 +85,22 @@ impl IndexerClient {
         tracing::debug!(indexed_block = indexed_block.unwrap_or("null"));
         let indexed_block = indexed_block.and_then(parse_graph_indexed_header);
 
+        // Fast-path rejection: check Content-Length header before reading body
+        let max_response_size = self.max_response_size;
+        if let Some(content_length) = response.headers().get(CONTENT_LENGTH)
+            && let Ok(len) = content_length.to_str().unwrap_or("0").parse::<usize>()
+            && len > max_response_size
+        {
+            return Err(BadResponse(format!(
+                "response too large: {len} bytes (max {max_response_size})"
+            )));
+        }
+
+        // Read body with size limit to prevent memory exhaustion
+        let body = read_body_limited(response, max_response_size)
+            .await
+            .map_err(BadResponse)?;
+
         #[derive(Debug, Deserialize)]
         pub struct IndexerResponsePayload {
             #[serde(rename = "graphQLResponse")]
@@ -86,10 +108,8 @@ impl IndexerClient {
             pub attestation: Option<Attestation>,
             pub error: Option<String>,
         }
-        let payload = response
-            .json::<IndexerResponsePayload>()
-            .await
-            .map_err(|err| BadResponse(err.to_string()))?;
+        let payload: IndexerResponsePayload =
+            serde_json::from_slice(&body).map_err(|err| BadResponse(err.to_string()))?;
         if let Some(err) = payload.error {
             return Err(BadResponse(err));
         }
@@ -208,6 +228,21 @@ fn check_block_error(err: &str) -> Result<(), MissingBlockError> {
     })
 }
 
+/// Read response body with size limit, streaming to avoid unbounded memory allocation.
+async fn read_body_limited(
+    mut response: reqwest::Response,
+    max_size: usize,
+) -> Result<Vec<u8>, String> {
+    let mut body = Vec::new();
+    while let Some(chunk) = response.chunk().await.map_err(|e| e.to_string())? {
+        if body.len() + chunk.len() > max_size {
+            return Err(format!("response exceeds {max_size} byte limit"));
+        }
+        body.extend_from_slice(&chunk);
+    }
+    Ok(body)
+}
+
 #[cfg(test)]
 mod tests {
     use crate::errors::MissingBlockError;
diff --git a/src/main.rs b/src/main.rs
index d2596b5b..d7532d37 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -109,6 +109,7 @@ async fn main() {
 
     let indexer_client = IndexerClient {
         client: http_client.clone(),
+        max_response_size: conf.max_indexer_response_size,
     };
     let network_subgraph_client = SubgraphClient {
         client: indexer_client.clone(),