diff --git a/crates/a11y/src/autotag.rs b/crates/a11y/src/autotag.rs
index b9ffa46669..5c0dc2bd19 100644
--- a/crates/a11y/src/autotag.rs
+++ b/crates/a11y/src/autotag.rs
@@ -66,7 +66,13 @@ fn content_bytes(doc: &Document, page: &pdfcraft_model::Page, index: usize) -> R
             if budget.remaining() == 0 {
                 unsupported(index, "decoding the content takes more than 16 MiB")
             } else {
-                unsupported(index, format!("content cannot be decoded strictly: {e}"))
+                // The decoder's own reason: `CosError::Filter`'s text would say again that the data
+                // couldn't be decoded.
+                let why = match e {
+                    pdfcraft_cos::CosError::Filter(why) => why,
+                    other => other.to_string(),
+                };
+                unsupported(index, format!("content cannot be decoded strictly: {why}"))
             }
         })?;
         all.extend_from_slice(&decoded);
diff --git a/crates/a11y/src/tests.rs b/crates/a11y/src/tests.rs
index 0ad6ecd3e5..960eb39d3d 100644
--- a/crates/a11y/src/tests.rs
+++ b/crates/a11y/src/tests.rs
@@ -113,7 +113,7 @@ fn autotag_text_reads_content_with_parameters_given_by_reference() {
 }
 
 /// Autotagging refuses a page whose content it can't read whole, and says why: content past
-/// 16 MiB, or content that doesn't decode strictly.
+/// 16 MiB, or content that doesn't decode strictly, with the decoder's reason right after.
 #[test]
 fn autotag_text_says_why_it_cannot_read_a_page() {
     use pdfcraft_cos::{Dict, ObjRef, Stream};
@@ -138,7 +138,7 @@ fn autotag_text_says_why_it_cannot_read_a_page() {
     let mut corrupt = Stream::from_raw(Dict::new(), b"not zlib data".to_vec());
     corrupt.dict.set(b"Filter".to_vec(), Object::name("FlateDecode"));
     let why = reason(corrupt);
-    assert!(why.starts_with("content cannot be decoded strictly"), "{why}");
+    assert!(why.starts_with("content cannot be decoded strictly: FlateDecode: "), "{why}");
 }
 
 #[test]