2 files changed, 9 insertions, 7 deletions
diff --git a/src/content/document.rs b/src/content/document.rs
index 7656db7..d2c2426 100644
--- a/src/content/document.rs
+++ b/src/content/document.rs
@@ -26,7 +26,6 @@ use crate::util::{
     skip,
     span::{from_exit_event, serialize},
 };
-use std::collections::HashSet;
 
 /// Phases where we can exit containers.
 #[derive(Debug, PartialEq)]
@@ -84,20 +83,24 @@ pub fn document(parse_state: &mut ParseState, point: Point, index: usize) -> Vec
     tokenizer.push(&parse_state.codes, Box::new(start), true);
 
     let mut index = 0;
-    let mut next_definitions: HashSet<String> = HashSet::new();
+    let mut next_definitions = vec![];
 
     while index < tokenizer.events.len() {
         let event = &tokenizer.events[index];
 
         if event.event_type == EventType::Exit && event.token_type == Token::DefinitionLabelString {
-            next_definitions.insert(normalize_identifier(
+            let id = normalize_identifier(
                 serialize(
                     &parse_state.codes,
                     &from_exit_event(&tokenizer.events, index),
                     false,
                 )
                 .as_str(),
-            ));
+            );
+
+            if !next_definitions.contains(&id) {
+                next_definitions.push(id);
+            }
         }
 
         index += 1;
diff --git a/src/parser.rs b/src/parser.rs
index 409e812..3361baf 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -4,7 +4,6 @@ use crate::content::document::document;
 use crate::tokenizer::{Code, Event, Point};
 use crate::util::codes::parse as parse_codes;
 use crate::{Constructs, Options};
-use std::collections::HashSet;
 
 /// Information needed, in all content types, when parsing markdown.
 ///
@@ -16,7 +15,7 @@ pub struct ParseState {
     /// List of codes.
     pub codes: Vec<Code>,
     /// Set of defined identifiers.
-    pub definitions: HashSet<String>,
+    pub definitions: Vec<String>,
 }
 
 /// Turn a string of markdown into events.
@@ -26,7 +25,7 @@ pub fn parse(value: &str, options: &Options) -> (Vec<Event>, ParseState) {
     let mut parse_state = ParseState {
         constructs: options.constructs.clone(),
         codes: parse_codes(value),
-        definitions: HashSet::new(),
+        definitions: vec![],
     };
 
     let events = document(