diff --git a/crates/pptx/src/custgeom.rs b/crates/pptx/src/custgeom.rs
index 981cb2e24..0eeb37cd5 100644
--- a/crates/pptx/src/custgeom.rs
+++ b/crates/pptx/src/custgeom.rs
@@ -15,6 +15,10 @@ use crate::xml::{A, El, W};
 
 const DEG: f64 = 60_000.0;
 
+/// Distinct path coordinate spaces whose guides are evaluated for one custom geometry; paths in
+/// further spaces are left out.
+const MAX_SPACES: usize = 16;
+
 /// Guide variables for one shape.
 pub struct Guides {
     vars: HashMap<String, f64>,
@@ -151,14 +155,24 @@ fn pt(g: &Guides, e: &El) -> (f64, f64) {
 pub fn read_cust_geom(cg: &El, w_emu: f64, h_emu: f64) -> Vec<CustomPath> {
     let mut out = vec![];
     let Some(pl) = cg.child("pathLst") else { return out };
+    let mut spaces: HashMap<(u64, u64), Guides> = HashMap::new();
     for p in pl.children_named("path").take(1000) {
         let pw = p.f64("w").unwrap_or(0.0);
         let ph = p.f64("h").unwrap_or(0.0);
         // Guides are evaluated in the path's own space when it has one.
         let (gw, gh) = if pw > 0.0 || ph > 0.0 { (pw, ph) } else { (w_emu, h_emu) };
-        let mut g = Guides::new(gw, gh);
-        g.eval_list(cg.child("avLst"));
-        g.eval_list(cg.child("gdLst"));
+        // The guide lists are evaluated once per coordinate space, not once per path.
+        let key = (gw.to_bits(), gh.to_bits());
+        if !spaces.contains_key(&key) {
+            if spaces.len() >= MAX_SPACES {
+                continue;
+            }
+            let mut g = Guides::new(gw, gh);
+            g.eval_list(cg.child("avLst"));
+            g.eval_list(cg.child("gdLst"));
+            spaces.insert(key, g);
+        }
+        let Some(g) = spaces.get(&key) else { continue };
         let mut d = String::new();
         let mut cur = (0.0, 0.0);
         let mut start = (0.0, 0.0);
@@ -166,7 +180,7 @@ pub fn read_cust_geom(cg: &El, w_emu: f64, h_emu: f64) -> Vec<CustomPath> {
             match c.local() {
                 "moveTo" => {
                     if let Some(q) = c.child("pt") {
-                        cur = pt(&g, q);
+                        cur = pt(g, q);
                         start = cur;
                         d.push_str("M ");
                         num(&mut d, cur.0);
@@ -177,7 +191,7 @@ pub fn read_cust_geom(cg: &El, w_emu: f64, h_emu: f64) -> Vec<CustomPath> {
                 }
                 "lnTo" => {
                     if let Some(q) = c.child("pt") {
-                        cur = pt(&g, q);
+                        cur = pt(g, q);
                         d.push_str("L ");
                         num(&mut d, cur.0);
                         d.push(' ');
@@ -186,7 +200,7 @@ pub fn read_cust_geom(cg: &El, w_emu: f64, h_emu: f64) -> Vec<CustomPath> {
                     }
                 }
                 "cubicBezTo" => {
-                    let pts: Vec<(f64, f64)> = c.children_named("pt").map(|q| pt(&g, q)).collect();
+                    let pts: Vec<(f64, f64)> = c.children_named("pt").map(|q| pt(g, q)).collect();
                     if let [a, b, e] = pts.as_slice() {
                         d.push_str("C ");
                         for (x, y) in [a, b, e] {
@@ -199,7 +213,7 @@ pub fn read_cust_geom(cg: &El, w_emu: f64, h_emu: f64) -> Vec<CustomPath> {
                     }
                 }
                 "quadBezTo" => {
-                    let pts: Vec<(f64, f64)> = c.children_named("pt").map(|q| pt(&g, q)).collect();
+                    let pts: Vec<(f64, f64)> = c.children_named("pt").map(|q| pt(g, q)).collect();
                     if let [a, e] = pts.as_slice() {
                         d.push_str("Q ");
                         for (x, y) in [a, e] {
@@ -470,6 +484,21 @@ mod tests {
         assert_eq!(paths[1].d, "M 1 1 Q 2 2 3 1");
     }
 
+    #[test]
+    fn paths_share_guides_and_distinct_spaces_are_capped() {
+        let path = |w: usize| format!(r#"<a:path w="{w}" h="10"><a:moveTo><a:pt x="mid" y="1"/></a:moveTo></a:path>"#);
+        let paths: String = (1..=40).map(|i| path(10 * i)).collect();
+        let x = format!(
+            r#"<a:custGeom xmlns:a="x"><a:gdLst><a:gd name="mid" fmla="*/ w 1 2"/></a:gdLst><a:pathLst>{paths}{}</a:pathLst></a:custGeom>"#,
+            path(10)
+        );
+        let d = parse(x.as_bytes()).unwrap();
+        let out = read_cust_geom(&d.root, 1.0, 1.0);
+        assert_eq!(out.len(), MAX_SPACES + 1, "16 spaces plus the repeat of the first");
+        assert!(out[0].d.starts_with("M 5 1"), "{}", out[0].d);
+        assert!(out[MAX_SPACES].d.starts_with("M 5 1"), "{}", out[MAX_SPACES].d);
+    }
+
     #[test]
     fn write_then_read_path() {
         let p = CustomPath { w: 100.0, h: 50.0, d: "M 0 0 L 100 0 C 100 10 90 50 50 50 Q 0 50 0 0 Z".into(), fill: FillMode::Norm, stroke: true };