diff --git a/crates/ruma-macros/Cargo.toml b/crates/ruma-macros/Cargo.toml
index 3fdb6dab..01a4f157 100644
--- a/crates/ruma-macros/Cargo.toml
+++ b/crates/ruma-macros/Cargo.toml
@@ -22,7 +22,6 @@ __internal_macro_expand = ["syn/visit-mut"]
 
 [dependencies]
 cfg-if = "1.0.0"
-once_cell = "1.13.0"
 proc-macro-crate = "3.1.0"
 proc-macro2 = "1.0.24"
 quote = "1.0.8"
diff --git a/crates/ruma-macros/src/api.rs b/crates/ruma-macros/src/api.rs
index d720577c..fdcfa80d 100644
--- a/crates/ruma-macros/src/api.rs
+++ b/crates/ruma-macros/src/api.rs
@@ -1,8 +1,7 @@
 //! Methods and types for generating API endpoints.
 
-use std::{env, fs, path::Path};
+use std::{env, fs, path::Path, sync::OnceLock};
 
-use once_cell::sync::Lazy;
 use proc_macro2::Span;
 use serde::{de::IgnoredAny, Deserialize};
 
@@ -29,37 +28,41 @@ fn ensure_feature_presence() -> Option<&'static syn::Error> {
         server: Option<IgnoredAny>,
     }
 
-    static RESULT: Lazy<Result<(), syn::Error>> = Lazy::new(|| {
-        let manifest_dir = env::var("CARGO_MANIFEST_DIR")
-            .map_err(|_| syn::Error::new(Span::call_site(), "Failed to read CARGO_MANIFEST_DIR"))?;
+    static RESULT: OnceLock<Result<(), syn::Error>> = OnceLock::new();
 
-        let manifest_file = Path::new(&manifest_dir).join("Cargo.toml");
-        let manifest_bytes = fs::read_to_string(manifest_file)
-            .map_err(|_| syn::Error::new(Span::call_site(), "Failed to read Cargo.toml"))?;
+    RESULT
+        .get_or_init(|| {
+            let manifest_dir = env::var("CARGO_MANIFEST_DIR").map_err(|_| {
+                syn::Error::new(Span::call_site(), "Failed to read CARGO_MANIFEST_DIR")
+            })?;
 
-        let manifest_parsed: CargoToml = toml::from_str(&manifest_bytes)
-            .map_err(|_| syn::Error::new(Span::call_site(), "Failed to parse Cargo.toml"))?;
+            let manifest_file = Path::new(&manifest_dir).join("Cargo.toml");
+            let manifest_bytes = fs::read_to_string(manifest_file)
+                .map_err(|_| syn::Error::new(Span::call_site(), "Failed to read Cargo.toml"))?;
 
-        if manifest_parsed.features.client.is_none() {
-            return Err(syn::Error::new(
-                Span::call_site(),
-                "This crate doesn't define a `client` feature in its `Cargo.toml`.\n\
+            let manifest_parsed: CargoToml = toml::from_str(&manifest_bytes)
+                .map_err(|_| syn::Error::new(Span::call_site(), "Failed to parse Cargo.toml"))?;
+
+            if manifest_parsed.features.client.is_none() {
+                return Err(syn::Error::new(
+                    Span::call_site(),
+                    "This crate doesn't define a `client` feature in its `Cargo.toml`.\n\
                  Please add a `client` feature such that generated `OutgoingRequest` and \
                  `IncomingResponse` implementations can be enabled.",
-            ));
-        }
+                ));
+            }
 
-        if manifest_parsed.features.server.is_none() {
-            return Err(syn::Error::new(
-                Span::call_site(),
-                "This crate doesn't define a `server` feature in its `Cargo.toml`.\n\
+            if manifest_parsed.features.server.is_none() {
+                return Err(syn::Error::new(
+                    Span::call_site(),
+                    "This crate doesn't define a `server` feature in its `Cargo.toml`.\n\
                  Please add a `server` feature such that generated `IncomingRequest` and \
                  `OutgoingResponse` implementations can be enabled.",
-            ));
-        }
+                ));
+            }
 
-        Ok(())
-    });
-
-    RESULT.as_ref().err()
+            Ok(())
+        })
+        .as_ref()
+        .err()
 }