diff --git a/crates/engine/src/fonts.rs b/crates/engine/src/fonts.rs
index e208f72c7..3d99d3f57 100644
--- a/crates/engine/src/fonts.rs
+++ b/crates/engine/src/fonts.rs
@@ -1,6 +1,8 @@
 //! Fonts a presentation uses that this machine doesn't have, so opening it can say so (its text
 //! draws in a stand-in; see `FontDb::document_face`).
 
+use std::collections::HashSet;
+
 use deckcraft_fonts::FontDb;
 use deckcraft_model::resolve::{self, Ctx};
 use deckcraft_model::text::{Bullet, TextBody};
@@ -12,8 +14,13 @@ use deckcraft_model::{Presentation, Shape, ShapeKind};
 /// font to load and are left for the round trip.
 pub fn install_embedded_fonts(p: &Presentation) {
     let db = FontDb::global();
+    // Faces can name one media item many times; each is copied and enumerated once.
+    let mut seen = HashSet::new();
     for font in &p.embedded_fonts {
         for id in font.faces().into_iter().flatten() {
+            if !seen.insert(id) {
+                continue;
+            }
             let Some(item) = p.media(id) else { continue };
             let Some(sfnt) = deckcraft_fonts::embedded_sfnt(&item.data) else { continue };
             db.add_font(sfnt.to_vec());
@@ -27,12 +34,8 @@ pub fn install_embedded_fonts(p: &Presentation) {
 /// and can't be installed, so they aren't reported.
 pub fn missing_fonts(p: &Presentation) -> Vec<String> {
     let db = FontDb::global();
-    let mut out: Vec<String> = Vec::new();
-    for family in used_fonts(p) {
-        if !family.starts_with('.') && !db.has_family(&family) && !out.iter().any(|f| f.eq_ignore_ascii_case(&family)) {
-            out.push(family);
-        }
-    }
+    // used_fonts is already free of case-insensitive duplicates.
+    let mut out: Vec<String> = used_fonts(p).into_iter().filter(|f| !f.starts_with('.') && !db.has_family(f)).collect();
     out.sort_by_key(|f| f.to_lowercase());
     out
 }
@@ -40,9 +43,10 @@ pub fn missing_fonts(p: &Presentation) -> Vec<String> {
 /// The families the slides' text runs and bullets are drawn in.
 pub fn used_fonts(p: &Presentation) -> Vec<String> {
     let mut out: Vec<String> = Vec::new();
+    let mut seen: HashSet<String> = HashSet::new();
     let mut add = |f: String| {
         let f = f.trim().to_string();
-        if !f.is_empty() && !out.iter().any(|o| o.eq_ignore_ascii_case(&f)) {
+        if !f.is_empty() && seen.insert(f.to_ascii_lowercase()) {
             out.push(f);
         }
     };
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 68de13418..2a1d174bb 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -6458,3 +6458,24 @@ fn master_body_placeholder_format_keeps_per_level_formatting() {
     assert_eq!((level(&s, 0).run.size, level(&s, 1).run.size), (Some(28.0), Some(24.0)));
     assert_eq!(shown(&s), vec![Some(28.0), Some(24.0)]);
 }
+
+#[test]
+fn many_distinct_fonts_are_listed_once_each_without_a_quadratic_scan() {
+    // 30,000 runs in 15,000 families, each written twice in different case.
+    let mut p = deckcraft_model::Presentation::default();
+    let slide = std::sync::Arc::make_mut(&mut p.slides[0]);
+    let mut body = deckcraft_model::text::TextBody::from_text("x");
+    let run = body.paragraphs[0].runs[0].clone();
+    body.paragraphs[0].runs = (0..30_000)
+        .map(|i| {
+            let mut r = run.clone();
+            let name = format!("Qqq Font {}", i / 2);
+            r.props.font = Some(if i % 2 == 0 { name } else { name.to_uppercase() });
+            r
+        })
+        .collect();
+    slide.shapes[0].text = Some(body);
+    let used = crate::fonts::used_fonts(&p);
+    assert_eq!(used.iter().filter(|f| f.starts_with("Qqq Font ")).count(), 15_000);
+    assert_eq!(crate::fonts::missing_fonts(&p).iter().filter(|f| f.to_ascii_lowercase().starts_with("qqq font ")).count(), 15_000);
+}