diff --git a/router/src/validation.rs b/router/src/validation.rs
index f82f9670..23f5e750 100644
--- a/router/src/validation.rs
+++ b/router/src/validation.rs
@@ -6,7 +6,6 @@ use crate::{
 };
 use base64::{engine::general_purpose::STANDARD, Engine};
 use image::{ImageFormat, ImageReader};
-use itertools::Itertools;
 use jsonschema::{Draft, JSONSchema};
 use rand::{thread_rng, Rng};
 use serde_json::Value;
@@ -720,15 +719,20 @@ fn prepare_input(
 
     // Replace image tokens by hashes. The first token of an image
     // must be specific to the image for prefix caching.
+    // TODO: disable when not caching prefixes.
     let mut token_ids = encoding.get_ids().to_owned();
     let mut iter = token_ids.iter_mut().filter(|id| **id == image_token_id);
     for (image_hash, n_tokens) in image_hashes.iter().zip(image_lens.iter()) {
-        let image_token = iter.next().ok_or(ValidationError::Tokenizer(
-            "Image token not found".to_string(),
-        ))?;
-        *image_token = *image_hash as u32;
-        // Skip the remaining tokens of the current image.
-        iter = iter.dropping(n_tokens - 1);
+        for i in 0..*n_tokens {
+            match iter.next() {
+                Some(image_token) => *image_token = *image_hash as u32 + i as u32,
+                None => {
+                    return Err(ValidationError::Tokenizer(
+                        "Image token not found".to_string(),
+                    ))
+                }
+            }
+        }
     }
 
     let encoding = Encoding::new(