diff --git a/examples/editor-libcosmic/src/main.rs b/examples/editor-libcosmic/src/main.rs
index a28f826..be2f89a 100644
--- a/examples/editor-libcosmic/src/main.rs
+++ b/examples/editor-libcosmic/src/main.rs
@@ -139,7 +139,10 @@ impl Application for Window {
             .family(cosmic_text::Family::Monospace);
 
         let mut editor = SyntaxEditor::new(
-            Buffer::new(&FONT_SYSTEM.lock().unwrap(), FontSize::Body.to_metrics()),
+            Buffer::new(
+                &mut FONT_SYSTEM.lock().unwrap(),
+                FontSize::Body.to_metrics(),
+            ),
             &SYNTAX_SYSTEM,
             "base16-eighties.dark",
         )
diff --git a/examples/editor-libcosmic/src/text.rs b/examples/editor-libcosmic/src/text.rs
index 76c1cea..f0c9c9a 100644
--- a/examples/editor-libcosmic/src/text.rs
+++ b/examples/editor-libcosmic/src/text.rs
@@ -53,7 +53,7 @@ impl Text {
         let mut line = BufferLine::new(string, AttrsList::new(Attrs::new()));
 
         //TODO: do we have to immediately shape?
-        line.shape(&FONT_SYSTEM.lock().unwrap());
+        line.shape(&mut FONT_SYSTEM.lock().unwrap());
 
         let text = Self {
             line,
@@ -186,7 +186,7 @@ where
                 };
 
                 cache.with_pixels(
-                    &FONT_SYSTEM.lock().unwrap(),
+                    &mut FONT_SYSTEM.lock().unwrap(),
                     cache_key,
                     glyph_color,
                     |pixel_x, pixel_y, color| {
diff --git a/examples/editor-orbclient/src/main.rs b/examples/editor-orbclient/src/main.rs
index 396be80..f784cee 100644
--- a/examples/editor-orbclient/src/main.rs
+++ b/examples/editor-orbclient/src/main.rs
@@ -58,7 +58,7 @@ fn main() {
     let line_x = 8.0 * display_scale;
 
     let mut editor = SyntaxEditor::new(
-        Buffer::new(&font_system, font_sizes[font_size_i]),
+        Buffer::new(&mut font_system, font_sizes[font_size_i]),
         &syntax_system,
         "base16-eighties.dark",
     )
diff --git a/examples/editor-test/src/main.rs b/examples/editor-test/src/main.rs
index 69a5498..ea859d5 100644
--- a/examples/editor-test/src/main.rs
+++ b/examples/editor-test/src/main.rs
@@ -60,7 +60,7 @@ fn main() {
     ];
     let font_size_default = 1; // Body
 
-    let mut buffer = Buffer::new(&font_system, font_sizes[font_size_default]);
+    let mut buffer = Buffer::new(&mut font_system, font_sizes[font_size_default]);
     buffer
         .borrow_with(&mut font_system)
         .set_size(window.width() as f32, window.height() as f32);
diff --git a/examples/rich-text/src/main.rs b/examples/rich-text/src/main.rs
index e8e8213..89bc450 100644
--- a/examples/rich-text/src/main.rs
+++ b/examples/rich-text/src/main.rs
@@ -37,7 +37,7 @@ fn main() {
     .unwrap();
 
     let mut editor = Editor::new(Buffer::new(
-        &font_system,
+        &mut font_system,
         Metrics::new(32.0, 44.0).scale(display_scale),
     ));
 
diff --git a/examples/terminal/src/main.rs b/examples/terminal/src/main.rs
index eae3ffe..852207f 100644
--- a/examples/terminal/src/main.rs
+++ b/examples/terminal/src/main.rs
@@ -15,7 +15,7 @@ fn main() {
     let metrics = Metrics::new(14.0, 20.0);
 
     // A Buffer provides shaping and layout for a UTF-8 string, create one per text widget
-    let mut buffer = Buffer::new(&font_system, metrics);
+    let mut buffer = Buffer::new(&mut font_system, metrics);
 
     let mut buffer = buffer.borrow_with(&mut font_system);
 
diff --git a/src/buffer.rs b/src/buffer.rs
index 937a60b..d8a67d4 100644
--- a/src/buffer.rs
+++ b/src/buffer.rs
@@ -317,7 +317,7 @@ impl Buffer {
     /// # Panics
     ///
     /// Will panic if `metrics.line_height` is zero.
-    pub fn new(font_system: &FontSystem, metrics: Metrics) -> Self {
+    pub fn new(font_system: &mut FontSystem, metrics: Metrics) -> Self {
         assert_ne!(metrics.line_height, 0.0, "line height cannot be 0");
 
         let mut buffer = Self {
@@ -343,7 +343,7 @@ impl Buffer {
         }
     }
 
-    pub(crate) fn relayout(&mut self, font_system: &FontSystem) {
+    pub(crate) fn relayout(&mut self, font_system: &mut FontSystem) {
         #[cfg(all(feature = "std", not(target_arch = "wasm32")))]
         let instant = std::time::Instant::now();
 
@@ -360,7 +360,7 @@ impl Buffer {
         log::debug!("relayout: {:?}", instant.elapsed());
     }
 
-    pub(crate) fn shape_until(&mut self, font_system: &FontSystem, lines: i32) -> i32 {
+    pub(crate) fn shape_until(&mut self, font_system: &mut FontSystem, lines: i32) -> i32 {
         #[cfg(all(feature = "std", not(target_arch = "wasm32")))]
         let instant = std::time::Instant::now();
 
@@ -387,7 +387,7 @@ impl Buffer {
         total_layout
     }
 
-    pub(crate) fn shape_until_cursor(&mut self, font_system: &FontSystem, cursor: Cursor) {
+    pub(crate) fn shape_until_cursor(&mut self, font_system: &mut FontSystem, cursor: Cursor) {
         #[cfg(all(feature = "std", not(target_arch = "wasm32")))]
         let instant = std::time::Instant::now();
 
@@ -427,7 +427,7 @@ impl Buffer {
         self.shape_until_scroll(font_system);
     }
 
-    pub(crate) fn shape_until_scroll(&mut self, font_system: &FontSystem) {
+    pub(crate) fn shape_until_scroll(&mut self, font_system: &mut FontSystem) {
         let lines = self.visible_lines();
 
         let scroll_end = self.scroll + lines;
@@ -468,7 +468,7 @@ impl Buffer {
 
     pub(crate) fn line_shape(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         line_i: usize,
     ) -> Option<&ShapeLine> {
         let line = self.lines.get_mut(line_i)?;
@@ -477,7 +477,7 @@ impl Buffer {
 
     pub(crate) fn line_layout(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         line_i: usize,
     ) -> Option<&[LayoutLine]> {
         let line = self.lines.get_mut(line_i)?;
@@ -489,7 +489,7 @@ impl Buffer {
         self.metrics
     }
 
-    fn set_metrics(&mut self, font_system: &FontSystem, metrics: Metrics) {
+    fn set_metrics(&mut self, font_system: &mut FontSystem, metrics: Metrics) {
         if metrics != self.metrics {
             assert_ne!(metrics.font_size, 0.0, "font size cannot be 0");
             self.metrics = metrics;
@@ -503,7 +503,7 @@ impl Buffer {
         self.wrap
     }
 
-    pub(crate) fn set_wrap(&mut self, font_system: &FontSystem, wrap: Wrap) {
+    pub(crate) fn set_wrap(&mut self, font_system: &mut FontSystem, wrap: Wrap) {
         if wrap != self.wrap {
             self.wrap = wrap;
             self.relayout(font_system);
@@ -516,7 +516,7 @@ impl Buffer {
         (self.width, self.height)
     }
 
-    pub(crate) fn set_size(&mut self, font_system: &FontSystem, width: f32, height: f32) {
+    pub(crate) fn set_size(&mut self, font_system: &mut FontSystem, width: f32, height: f32) {
         let clamped_width = width.max(0.0);
         let clamped_height = height.max(0.0);
 
@@ -546,7 +546,7 @@ impl Buffer {
         (self.height / self.metrics.line_height) as i32
     }
 
-    pub(crate) fn set_text(&mut self, font_system: &FontSystem, text: &str, attrs: Attrs) {
+    pub(crate) fn set_text(&mut self, font_system: &mut FontSystem, text: &str, attrs: Attrs) {
         self.lines.clear();
         for line in text.lines() {
             self.lines
@@ -682,7 +682,7 @@ impl Buffer {
     #[cfg(feature = "swash")]
     pub(crate) fn draw<F>(
         &self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache: &mut crate::SwashCache,
         color: Color,
         mut f: F,
@@ -758,7 +758,7 @@ impl<'a> BorrowedWithFontSystem<'a, Buffer> {
 
     /// Draw the buffer
     #[cfg(feature = "swash")]
-    pub fn draw<F>(&self, cache: &mut crate::SwashCache, color: Color, f: F)
+    pub fn draw<F>(&mut self, cache: &mut crate::SwashCache, color: Color, f: F)
     where
         F: FnMut(i32, i32, u32, u32, Color),
     {
diff --git a/src/buffer_line.rs b/src/buffer_line.rs
index e9b7e0b..3ff511a 100644
--- a/src/buffer_line.rs
+++ b/src/buffer_line.rs
@@ -167,7 +167,7 @@ impl BufferLine {
     }
 
     /// Shape line, will cache results
-    pub fn shape(&mut self, font_system: &FontSystem) -> &ShapeLine {
+    pub fn shape(&mut self, font_system: &mut FontSystem) -> &ShapeLine {
         if self.shape_opt.is_none() {
             self.shape_opt = Some(ShapeLine::new(font_system, &self.text, &self.attrs_list));
             self.layout_opt = None;
@@ -183,7 +183,7 @@ impl BufferLine {
     /// Layout line, will cache results
     pub fn layout(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         font_size: f32,
         width: f32,
         wrap: Wrap,
diff --git a/src/edit/editor.rs b/src/edit/editor.rs
index d97216e..a0987e3 100644
--- a/src/edit/editor.rs
+++ b/src/edit/editor.rs
@@ -35,7 +35,7 @@ impl Editor {
         }
     }
 
-    fn set_layout_cursor(&mut self, font_system: &FontSystem, cursor: LayoutCursor) {
+    pub(crate) fn set_layout_cursor(&mut self, font_system: &mut FontSystem, cursor: LayoutCursor) {
         let layout = self
             .buffer
             .line_layout(font_system, cursor.line)
@@ -94,7 +94,7 @@ impl Edit for Editor {
         }
     }
 
-    fn shape_as_needed(&mut self, font_system: &FontSystem) {
+    fn shape_as_needed(&mut self, font_system: &mut FontSystem) {
         if self.cursor_moved {
             self.buffer.shape_until_cursor(font_system, self.cursor);
             self.cursor_moved = false;
@@ -281,7 +281,7 @@ impl Edit for Editor {
         self.cursor.index = self.buffer.lines[self.cursor.line].text().len() - after_len;
     }
 
-    fn action(&mut self, font_system: &FontSystem, action: Action) {
+    fn action(&mut self, font_system: &mut FontSystem, action: Action) {
         let old_cursor = self.cursor;
 
         match action {
@@ -677,7 +677,7 @@ impl Edit for Editor {
     #[cfg(feature = "swash")]
     fn draw<F>(
         &self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache: &mut crate::SwashCache,
         color: Color,
         mut f: F,
diff --git a/src/edit/mod.rs b/src/edit/mod.rs
index b7ddee8..4cd1b2b 100644
--- a/src/edit/mod.rs
+++ b/src/edit/mod.rs
@@ -108,7 +108,7 @@ pub trait Edit {
     fn set_select_opt(&mut self, select_opt: Option<Cursor>);
 
     /// Shape lines until scroll, after adjusting scroll if the cursor moved
-    fn shape_as_needed(&mut self, font_system: &FontSystem);
+    fn shape_as_needed(&mut self, font_system: &mut FontSystem);
 
     /// Copy selection
     fn copy_selection(&mut self) -> Option<String>;
@@ -122,12 +122,17 @@ pub trait Edit {
     fn insert_string(&mut self, data: &str, attrs_list: Option<AttrsList>);
 
     /// Perform an [Action] on the editor
-    fn action(&mut self, font_system: &FontSystem, action: Action);
+    fn action(&mut self, font_system: &mut FontSystem, action: Action);
 
     /// Draw the editor
     #[cfg(feature = "swash")]
-    fn draw<F>(&self, font_system: &FontSystem, cache: &mut crate::SwashCache, color: Color, f: F)
-    where
+    fn draw<F>(
+        &self,
+        font_system: &mut FontSystem,
+        cache: &mut crate::SwashCache,
+        color: Color,
+        f: F,
+    ) where
         F: FnMut(i32, i32, u32, u32, Color);
 }
 
@@ -152,7 +157,7 @@ impl<'a, T: Edit> BorrowedWithFontSystem<'a, T> {
 
     /// Draw the editor
     #[cfg(feature = "swash")]
-    pub fn draw<F>(&self, cache: &mut crate::SwashCache, color: Color, f: F)
+    pub fn draw<F>(&mut self, cache: &mut crate::SwashCache, color: Color, f: F)
     where
         F: FnMut(i32, i32, u32, u32, Color),
     {
diff --git a/src/edit/syntect.rs b/src/edit/syntect.rs
index 7c7e3da..c1d8dea 100644
--- a/src/edit/syntect.rs
+++ b/src/edit/syntect.rs
@@ -63,7 +63,7 @@ impl<'a> SyntaxEditor<'a> {
     #[cfg(feature = "std")]
     pub(crate) fn load_text<P: AsRef<Path>>(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         path: P,
         attrs: crate::Attrs,
     ) -> io::Result<()> {
@@ -131,7 +131,7 @@ impl<'a> Edit for SyntaxEditor<'a> {
         self.editor.set_select_opt(select_opt);
     }
 
-    fn shape_as_needed(&mut self, font_system: &FontSystem) {
+    fn shape_as_needed(&mut self, font_system: &mut FontSystem) {
         #[cfg(feature = "std")]
         let now = std::time::Instant::now();
 
@@ -236,7 +236,7 @@ impl<'a> Edit for SyntaxEditor<'a> {
         self.editor.insert_string(data, attrs_list);
     }
 
-    fn action(&mut self, font_system: &FontSystem, action: Action) {
+    fn action(&mut self, font_system: &mut FontSystem, action: Action) {
         self.editor.action(font_system, action);
     }
 
@@ -244,7 +244,7 @@ impl<'a> Edit for SyntaxEditor<'a> {
     #[cfg(feature = "swash")]
     fn draw<F>(
         &self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache: &mut crate::SwashCache,
         _color: Color,
         mut f: F,
diff --git a/src/edit/vi.rs b/src/edit/vi.rs
index e1ef722..666d4db 100644
--- a/src/edit/vi.rs
+++ b/src/edit/vi.rs
@@ -32,7 +32,7 @@ impl<'a> ViEditor<'a> {
     #[cfg(feature = "std")]
     pub(crate) fn load_text<P: AsRef<std::path::Path>>(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         path: P,
         attrs: crate::Attrs,
     ) -> std::io::Result<()> {
@@ -71,7 +71,7 @@ impl<'a> Edit for ViEditor<'a> {
         self.editor.set_select_opt(select_opt);
     }
 
-    fn shape_as_needed(&mut self, font_system: &FontSystem) {
+    fn shape_as_needed(&mut self, font_system: &mut FontSystem) {
         self.editor.shape_as_needed(font_system);
     }
 
@@ -87,7 +87,7 @@ impl<'a> Edit for ViEditor<'a> {
         self.editor.insert_string(data, attrs_list);
     }
 
-    fn action(&mut self, font_system: &FontSystem, action: Action) {
+    fn action(&mut self, font_system: &mut FontSystem, action: Action) {
         let old_mode = self.mode;
 
         match self.mode {
@@ -229,7 +229,7 @@ impl<'a> Edit for ViEditor<'a> {
     #[cfg(feature = "swash")]
     fn draw<F>(
         &self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache: &mut crate::SwashCache,
         color: Color,
         mut f: F,
diff --git a/src/font/system/no_std.rs b/src/font/system/no_std.rs
index 70318f6..e402615 100644
--- a/src/font/system/no_std.rs
+++ b/src/font/system/no_std.rs
@@ -44,24 +44,17 @@ impl FontSystem {
     }
 
     pub fn get_font(&self, id: fontdb::ID) -> Option<Arc<Font>> {
-        let face = self.db.face(id)?;
-        match Font::new(face) {
-            Some(font) => Some(Arc::new(font)),
-            None => {
-                log::warn!("failed to load font '{}'", face.post_script_name);
-                None
-            }
-        }
+        get_font(&self.db, id)
     }
 
-    pub fn get_font_matches(&self, attrs: Attrs) -> Arc<Vec<Arc<Font>>> {
+    pub fn get_font_matches(&mut self, attrs: Attrs) -> Arc<Vec<Arc<Font>>> {
         let mut fonts = Vec::new();
         for face in self.db.faces() {
             if !attrs.matches(face) {
                 continue;
             }
 
-            if let Some(font) = self.get_font(face.id) {
+            if let Some(font) = get_font(&self.db, face.id) {
                 fonts.push(font);
             }
         }
@@ -69,3 +62,14 @@ impl FontSystem {
         Arc::new(fonts)
     }
 }
+
+fn get_font(db: &fontdb::Database, id: fontdb::ID) -> Option<Arc<Font>> {
+    let face = db.face(id)?;
+    match Font::new(face) {
+        Some(font) => Some(Arc::new(font)),
+        None => {
+            log::warn!("failed to load font '{}'", face.post_script_name);
+            None
+        }
+    }
+}
diff --git a/src/font/system/std.rs b/src/font/system/std.rs
index 3f8e0e0..7ac5cbe 100644
--- a/src/font/system/std.rs
+++ b/src/font/system/std.rs
@@ -1,9 +1,6 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
-use std::{
-    collections::HashMap,
-    sync::{Arc, Mutex},
-};
+use std::{collections::HashMap, sync::Arc};
 
 use crate::{Attrs, AttrsOwned, Font};
 
@@ -11,8 +8,8 @@ use crate::{Attrs, AttrsOwned, Font};
 pub struct FontSystem {
     locale: String,
     db: fontdb::Database,
-    font_cache: Mutex<HashMap<fontdb::ID, Option<Arc<Font>>>>,
-    font_matches_cache: Mutex<HashMap<AttrsOwned, Arc<Vec<Arc<Font>>>>>,
+    font_cache: HashMap<fontdb::ID, Option<Arc<Font>>>,
+    font_matches_cache: HashMap<AttrsOwned, Arc<Vec<Arc<Font>>>>,
 }
 
 impl FontSystem {
@@ -88,8 +85,8 @@ impl FontSystem {
         Self {
             locale,
             db,
-            font_cache: Mutex::new(HashMap::new()),
-            font_matches_cache: Mutex::new(HashMap::new()),
+            font_cache: HashMap::new(),
+            font_matches_cache: HashMap::new(),
         }
     }
 
@@ -105,44 +102,28 @@ impl FontSystem {
         (self.locale, self.db)
     }
 
-    pub fn get_font(&self, id: fontdb::ID) -> Option<Arc<Font>> {
-        self.font_cache
-            .lock()
-            .expect("failed to lock font cache")
-            .entry(id)
-            .or_insert_with(|| {
-                let face = self.db.face(id)?;
-                match Font::new(face) {
-                    Some(font) => Some(Arc::new(font)),
-                    None => {
-                        log::warn!("failed to load font '{}'", face.post_script_name);
-                        None
-                    }
-                }
-            })
-            .clone()
+    pub fn get_font(&mut self, id: fontdb::ID) -> Option<Arc<Font>> {
+        get_font(&mut self.font_cache, &mut self.db, id)
     }
 
-    pub fn get_font_matches(&self, attrs: Attrs) -> Arc<Vec<Arc<Font>>> {
+    pub fn get_font_matches(&mut self, attrs: Attrs) -> Arc<Vec<Arc<Font>>> {
         self.font_matches_cache
-            .lock()
-            .expect("failed to lock font matches cache")
             //TODO: do not create AttrsOwned unless entry does not already exist
             .entry(AttrsOwned::new(attrs))
             .or_insert_with(|| {
                 #[cfg(not(target_arch = "wasm32"))]
                 let now = std::time::Instant::now();
 
-                let mut fonts = Vec::new();
-                for face in self.db.faces() {
-                    if !attrs.matches(face) {
-                        continue;
-                    }
-
-                    if let Some(font) = self.get_font(face.id) {
-                        fonts.push(font);
-                    }
-                }
+                let ids = self
+                    .db
+                    .faces()
+                    .filter(|face| attrs.matches(face))
+                    .map(|face| face.id)
+                    .collect::<Vec<_>>();
+                let fonts = ids
+                    .into_iter()
+                    .filter_map(|id| get_font(&mut self.font_cache, &mut self.db, id))
+                    .collect();
 
                 #[cfg(not(target_arch = "wasm32"))]
                 {
@@ -155,3 +136,23 @@ impl FontSystem {
             .clone()
     }
 }
+
+fn get_font(
+    font_cache: &mut HashMap<fontdb::ID, Option<Arc<Font>>>,
+    db: &mut fontdb::Database,
+    id: fontdb::ID,
+) -> Option<Arc<Font>> {
+    font_cache
+        .entry(id)
+        .or_insert_with(|| {
+            let face = db.face(id)?;
+            match Font::new(face) {
+                Some(font) => Some(Arc::new(font)),
+                None => {
+                    log::warn!("failed to load font '{}'", face.post_script_name);
+                    None
+                }
+            }
+        })
+        .clone()
+}
diff --git a/src/shape.rs b/src/shape.rs
index 4cc0346..dae7bc5 100644
--- a/src/shape.rs
+++ b/src/shape.rs
@@ -99,7 +99,7 @@ fn shape_fallback(
 }
 
 fn shape_run(
-    font_system: &FontSystem,
+    font_system: &mut FontSystem,
     line: &str,
     attrs_list: &AttrsList,
     start_run: usize,
@@ -273,7 +273,7 @@ pub struct ShapeWord {
 
 impl ShapeWord {
     pub fn new(
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         line: &str,
         attrs_list: &AttrsList,
         word_range: Range<usize>,
@@ -347,7 +347,7 @@ pub struct ShapeSpan {
 
 impl ShapeSpan {
     pub fn new(
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         line: &str,
         attrs_list: &AttrsList,
         span_range: Range<usize>,
@@ -431,7 +431,7 @@ impl ShapeLine {
     /// # Panics
     ///
     /// Will panic if `line` contains more than one paragraph.
-    pub fn new(font_system: &FontSystem, line: &str, attrs_list: &AttrsList) -> Self {
+    pub fn new(font_system: &mut FontSystem, line: &str, attrs_list: &AttrsList) -> Self {
         let mut spans = Vec::new();
 
         let bidi = unicode_bidi::BidiInfo::new(line, None);
diff --git a/src/swash.rs b/src/swash.rs
index f951c3e..363c900 100644
--- a/src/swash.rs
+++ b/src/swash.rs
@@ -16,7 +16,7 @@ pub use swash::scale::image::{Content as SwashContent, Image as SwashImage};
 pub use swash::zeno::{Command, Placement};
 
 fn swash_image(
-    font_system: &FontSystem,
+    font_system: &mut FontSystem,
     context: &mut ScaleContext,
     cache_key: CacheKey,
 ) -> Option<SwashImage> {
@@ -57,7 +57,7 @@ fn swash_image(
 }
 
 fn swash_outline_commands(
-    font_system: &FontSystem,
+    font_system: &mut FontSystem,
     context: &mut ScaleContext,
     cache_key: CacheKey,
 ) -> Option<Vec<swash::zeno::Command>> {
@@ -109,7 +109,7 @@ impl SwashCache {
     /// Create a swash Image from a cache key, without caching results
     pub fn get_image_uncached(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache_key: CacheKey,
     ) -> Option<SwashImage> {
         swash_image(font_system, &mut self.context, cache_key)
@@ -118,7 +118,7 @@ impl SwashCache {
     /// Create a swash Image from a cache key, caching results
     pub fn get_image(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache_key: CacheKey,
     ) -> &Option<SwashImage> {
         self.image_cache
@@ -128,7 +128,7 @@ impl SwashCache {
 
     pub fn get_outline_commands(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache_key: CacheKey,
     ) -> Option<&[swash::zeno::Command]> {
         self.outline_command_cache
@@ -140,7 +140,7 @@ impl SwashCache {
     /// Enumerate pixels in an Image, use `with_image` for better performance
     pub fn with_pixels<F: FnMut(i32, i32, Color)>(
         &mut self,
-        font_system: &FontSystem,
+        font_system: &mut FontSystem,
         cache_key: CacheKey,
         base: Color,
         mut f: F,