diff --git a/src/cli/self_update/unix.rs b/src/cli/self_update/unix.rs
index 7edcd68b78..e594336675 100644
--- a/src/cli/self_update/unix.rs
+++ b/src/cli/self_update/unix.rs
@@ -56,10 +56,7 @@ pub(crate) fn do_remove_from_path(process: &Process) -> Result<()> {
             let file = utils::read_file("rcfile", rc)?;
             let file_bytes = file.into_bytes();
             // FIXME: This is whitespace sensitive where it should not be.
-            if let Some(idx) = file_bytes
-                .windows(source_bytes.len())
-                .position(|w| w == source_bytes.as_slice())
-            {
+            if let Some(idx) = find_exact_line(&file_bytes, &source_bytes) {
                 // Here we rewrite the file without the offending line.
                 let mut new_bytes = file_bytes[..idx].to_vec();
                 new_bytes.extend(&file_bytes[idx + source_bytes.len()..]);
@@ -148,10 +145,7 @@ fn remove_legacy_source_command(source_cmd: String, process: &Process) -> Result
         let file = utils::read_file("rcfile", &rc)?;
         let file_bytes = file.into_bytes();
         // FIXME: This is whitespace sensitive where it should not be.
-        if let Some(idx) = file_bytes
-            .windows(cmd_bytes.len())
-            .position(|w| w == cmd_bytes.as_slice())
-        {
+        if let Some(idx) = find_exact_line(&file_bytes, &cmd_bytes) {
             // Here we rewrite the file without the offending line.
             let mut new_bytes = file_bytes[..idx].to_vec();
             new_bytes.extend(&file_bytes[idx + cmd_bytes.len()..]);
@@ -162,6 +156,16 @@ fn remove_legacy_source_command(source_cmd: String, process: &Process) -> Result
     Ok(())
 }
 
+fn find_exact_line(file: &[u8], line: &[u8]) -> Option<usize> {
+    // The trailing newline enforces the end boundary; check the start boundary here.
+    assert!(line.ends_with(b"\n"));
+    file.windows(line.len())
+        .enumerate()
+        .find_map(|(idx, candidate)| {
+            (candidate == line && (idx == 0 || file[idx - 1] == b'\n')).then_some(idx)
+        })
+}
+
 fn remove_legacy_paths(process: &Process) -> Result<()> {
     // Before the work to support more kinds of shells, which was released in
     // version 1.23.0 of Rustup, we always inserted this line instead, which is
diff --git a/tests/suite/cli_paths.rs b/tests/suite/cli_paths.rs
index 65b6170aab..b8a5e70dde 100644
--- a/tests/suite/cli_paths.rs
+++ b/tests/suite/cli_paths.rs
@@ -383,6 +383,41 @@ error: could not amend shell profile[..]
         }
     }
 
+    #[tokio::test]
+    async fn install_preserves_guarded_legacy_source() {
+        let cx = CliTestContext::new(Scenario::Empty).await;
+        let profile = cx.config.homedir.join(".bash_profile");
+        let guarded_source = "[ -f \"$HOME/.cargo/env\" ] && source \"$HOME/.cargo/env\"\n";
+        raw::write_file(&profile, guarded_source).unwrap();
+
+        let mut cmd = cx.config.cmd("rustup-init", &INIT_NONE[1..]);
+        cmd.env_remove("CARGO_HOME");
+        assert!(cmd.output().unwrap().status.success());
+
+        let new_profile = fs::read_to_string(&profile).unwrap();
+        let expected = guarded_source.to_owned() + &source("$HOME/.cargo", POSIX_SH);
+        assert_eq!(new_profile, expected);
+    }
+
+    #[tokio::test]
+    async fn uninstall_preserves_guarded_source() {
+        let cx = CliTestContext::new(Scenario::Empty).await;
+        let profile = cx.config.homedir.join(".bash_profile");
+        let guarded_source = "[ -f \"$HOME/.cargo/env\" ] && . \"$HOME/.cargo/env\"\n";
+        raw::write_file(&profile, guarded_source).unwrap();
+
+        let mut cmd = cx.config.cmd("rustup-init", &INIT_NONE[1..]);
+        cmd.env_remove("CARGO_HOME");
+        assert!(cmd.output().unwrap().status.success());
+
+        let mut cmd = cx.config.cmd("rustup", ["self", "uninstall", "-y"]);
+        cmd.env_remove("CARGO_HOME");
+        assert!(cmd.output().unwrap().status.success());
+
+        let new_profile = fs::read_to_string(&profile).unwrap();
+        assert_eq!(new_profile, guarded_source);
+    }
+
     #[tokio::test]
     async fn uninstall_cleans_up_legacy_paths() {
         let cx = CliTestContext::new(Scenario::Empty).await;