diff --git a/fuzz/fuzz.rs b/fuzz/fuzz.rs
index 4e48f1d..610e08b 100644
--- a/fuzz/fuzz.rs
+++ b/fuzz/fuzz.rs
@@ -68,19 +68,30 @@ pub unsafe extern "C" fn LLVMFuzzerTestOneInput(input: *const u8, len: usize) ->
         result => panic!("got unexpected result from python: {result}"),
     };
 
-    let gentoo_utils_result = Atom::parser().check_finished(InputIter::new(atom)).is_ok();
+    let gentoo_utils_result = Atom::parser().parse_finished(InputIter::new(atom));
 
     match (portage_result, gentoo_utils_result) {
-        (true, true) => {
+        (true, Ok(_)) => {
             eprintln!("agreement that {atom} is valid");
         }
-        (false, false) => {
+        (false, Err(_)) => {
             eprintln!("agreement that {atom} is invalid");
         }
-        (true, false) => {
+        (true, Err(_)) => {
             panic!("rejected valid atom: {atom}");
         }
-        (false, true) => {
+        (false, Ok(atom))
+            if atom.usedeps().iter().any(|usedep| {
+                atom.usedeps()
+                    .iter()
+                    .filter(|u| usedep.flag() == u.flag())
+                    .count()
+                    > 1
+            }) =>
+        {
+            eprintln!("disagreement due to duplicates in usedeps");
+        }
+        (false, Ok(_)) => {
             panic!("accpeted invalid atom: {atom}")
         }
     }