diff --git a/rust/src/managed-engine/src/process.rs b/rust/src/managed-engine/src/process.rs
index cf247c3b86..1f0b9f86b2 100644
--- a/rust/src/managed-engine/src/process.rs
+++ b/rust/src/managed-engine/src/process.rs
@@ -54,6 +54,14 @@ impl ManagedEngineConfig {
         format!("tcp://{}:{}", self.handshake_host, self.handshake_port)
     }
 
+    /// Env vars every managed engine needs when serving the Rust frontend:
+    /// `VLLM_USE_RUST_FRONTEND=1` tells Python vLLM to keep frontend-side
+    /// multimodal normalization (`mm_device_do_normalize = False`,
+    /// vllm/config/model.py) instead of expecting raw uint8 pixels.
+    pub fn rust_frontend_envs() -> Vec<(String, String)> {
+        vec![("VLLM_USE_RUST_FRONTEND".to_string(), "1".to_string())]
+    }
+
     /// Build the concrete Python command line for the managed headless engine.
     pub fn to_command(&self) -> StdCommand {
         let mut command = StdCommand::new(&self.python);
@@ -70,6 +78,7 @@ impl ManagedEngineConfig {
             .arg("--data-parallel-size")
             .arg(self.data_parallel_size.to_string())
             .args(&self.python_args);
+        command.envs(Self::rust_frontend_envs());
         command
     }
 }
@@ -256,6 +265,32 @@ mod tests {
             ]
         "#]]
         .assert_debug_eq(&args);
+
+        let envs = command.get_envs().collect::<Vec<_>>();
+        expect![[r#"
+            [
+                (
+                    "VLLM_USE_RUST_FRONTEND",
+                    Some(
+                        "1",
+                    ),
+                ),
+            ]
+        "#]]
+        .assert_debug_eq(&envs);
+    }
+
+    #[test]
+    fn rust_frontend_envs_include_rust_frontend_flag() {
+        expect![[r#"
+            [
+                (
+                    "VLLM_USE_RUST_FRONTEND",
+                    "1",
+                ),
+            ]
+        "#]]
+        .assert_debug_eq(&ManagedEngineConfig::rust_frontend_envs());
     }
 
     #[test]