diff --git a/Cargo.toml b/Cargo.toml
index c93a5705..4d10883b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -28,6 +28,7 @@ empty_structs_with_brackets = "warn"
 error_impl_error = "warn"
 filetype_is_file = "warn"
 float_cmp_const = "warn"
+format_push_string = "warn"
 get_unwrap = "warn"
 lossy_float_literal = "warn"
 mem_forget = "warn"
diff --git a/src/config.rs b/src/config.rs
index f10819b5..539a26f9 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,6 +1,7 @@
 use std::{
     collections::BTreeMap,
     fmt,
+    fmt::Write,
     net::{IpAddr, Ipv4Addr},
 };
 
@@ -191,7 +192,8 @@ impl fmt::Display for Config {
         let mut msg: String = "Active config values:\n\n".to_owned();
 
         for line in lines.into_iter().enumerate() {
-            msg += &format!("{}: {}\n", line.1 .0, line.1 .1);
+            writeln!(msg, "{}: {}", line.1 .0, line.1 .1)
+                .expect("write to in-memory buffer should succeed");
         }
 
         write!(f, "{msg}")
diff --git a/src/service/admin.rs b/src/service/admin.rs
index f61938a1..f3cd40fc 100644
--- a/src/service/admin.rs
+++ b/src/service/admin.rs
@@ -1,6 +1,7 @@
 use std::{
     collections::BTreeMap,
     convert::{TryFrom, TryInto},
+    fmt::Write,
     sync::Arc,
     time::Instant,
 };
@@ -413,13 +414,13 @@ impl Service {
 
                 for (r, (e, i)) in map.iter() {
                     let elapsed = i.elapsed();
-                    msg += &format!(
-                        "{} {}: {}m{}s\n",
-                        r,
-                        e,
+                    writeln!(
+                        msg,
+                        "{r} {e}: {}m{}s",
                         elapsed.as_secs() / 60,
                         elapsed.as_secs() % 60
-                    );
+                    )
+                    .expect("write to in-memory buffer should succeed");
                 }
                 RoomMessageEventContent::text_plain(&msg)
             }
@@ -718,8 +719,10 @@ impl Service {
                         markdown_message.push_str("The following user ids are not valid:\n```\n");
                         html_message.push_str("The following user ids are not valid:\n<pre>\n");
                         for invalid_user in invalid_users {
-                            markdown_message.push_str(&format!("{invalid_user}\n"));
-                            html_message.push_str(&format!("{invalid_user}\n"));
+                            writeln!(markdown_message, "{invalid_user}")
+                                .expect("write to in-memory buffer should succeed");
+                            writeln!(html_message, "{invalid_user}")
+                                .expect("write to in-memory buffer should succeed");
                         }
                         markdown_message.push_str("```\n\n");
                         html_message.push_str("</pre>\n\n");
@@ -730,8 +733,10 @@ impl Service {
                         html_message
                             .push_str("The following users are not from this server:\n<pre>\n");
                         for remote_id in remote_ids {
-                            markdown_message.push_str(&format!("{remote_id}\n"));
-                            html_message.push_str(&format!("{remote_id}\n"));
+                            writeln!(markdown_message, "{remote_id}")
+                                .expect("write to in-memory buffer should succeed");
+                            writeln!(html_message, "{remote_id}")
+                                .expect("write to in-memory buffer should succeed");
                         }
                         markdown_message.push_str("```\n\n");
                         html_message.push_str("</pre>\n\n");
@@ -740,8 +745,10 @@ impl Service {
                         markdown_message.push_str("The following users do not exist:\n```\n");
                         html_message.push_str("The following users do not exist:\n<pre>\n");
                         for non_existant_id in non_existant_ids {
-                            markdown_message.push_str(&format!("{non_existant_id}\n"));
-                            html_message.push_str(&format!("{non_existant_id}\n"));
+                            writeln!(markdown_message, "{non_existant_id}")
+                                .expect("write to in-memory buffer should succeed");
+                            writeln!(html_message, "{non_existant_id}")
+                                .expect("write to in-memory buffer should succeed");
                         }
                         markdown_message.push_str("```\n\n");
                         html_message.push_str("</pre>\n\n");