diff --git a/clippy_lints/src/let_underscore.rs b/clippy_lints/src/let_underscore.rs
index 4d746596c377..a43674316a1e 100644
--- a/clippy_lints/src/let_underscore.rs
+++ b/clippy_lints/src/let_underscore.rs
@@ -80,7 +80,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetUnderscore {
                             cx,
                             LET_UNDERSCORE_LOCK,
                             stmt.span,
-                            "non-binding let on an a synchronization lock",
+                            "non-binding let on a synchronization lock",
                             "consider using an underscore-prefixed named binding"
                         )
                     } else {
diff --git a/tests/ui/let_underscore_lock.rs b/tests/ui/let_underscore_lock.rs
new file mode 100644
index 000000000000..f4a33c360660
--- /dev/null
+++ b/tests/ui/let_underscore_lock.rs
@@ -0,0 +1,10 @@
+#![warn(clippy::let_underscore_lock)]
+
+fn main() {
+    let m = std::sync::Mutex::new(());
+    let rw = std::sync::RwLock::new(());
+
+    let _ = m.lock();
+    let _ = rw.read();
+    let _ = rw.write();
+}
diff --git a/tests/ui/let_underscore_lock.stderr b/tests/ui/let_underscore_lock.stderr
new file mode 100644
index 000000000000..bd297f6020cc
--- /dev/null
+++ b/tests/ui/let_underscore_lock.stderr
@@ -0,0 +1,27 @@
+error: non-binding let on a synchronization lock
+  --> $DIR/let_underscore_lock.rs:7:5
+   |
+LL |     let _ = m.lock();
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::let-underscore-lock` implied by `-D warnings`
+   = help: consider using an underscore-prefixed named binding
+
+error: non-binding let on a synchronization lock
+  --> $DIR/let_underscore_lock.rs:8:5
+   |
+LL |     let _ = rw.read();
+   |     ^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider using an underscore-prefixed named binding
+
+error: non-binding let on a synchronization lock
+  --> $DIR/let_underscore_lock.rs:9:5
+   |
+LL |     let _ = rw.write();
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider using an underscore-prefixed named binding
+
+error: aborting due to 3 previous errors
+
diff --git a/tests/ui/let_underscore.rs b/tests/ui/let_underscore_must_use.rs
similarity index 88%
rename from tests/ui/let_underscore.rs
rename to tests/ui/let_underscore_must_use.rs
index cfe207251f47..7f481542fa73 100644
--- a/tests/ui/let_underscore.rs
+++ b/tests/ui/let_underscore_must_use.rs
@@ -88,11 +88,4 @@ fn main() {
     let _ = a.map(|_| ());
 
     let _ = a;
-
-    let m = std::sync::Mutex::new(());
-    let rw = std::sync::RwLock::new(());
-
-    let _ = m.lock();
-    let _ = rw.read();
-    let _ = rw.write();
 }
diff --git a/tests/ui/let_underscore.stderr b/tests/ui/let_underscore_must_use.stderr
similarity index 66%
rename from tests/ui/let_underscore.stderr
rename to tests/ui/let_underscore_must_use.stderr
index bcd560fe493f..447f2419e3bd 100644
--- a/tests/ui/let_underscore.stderr
+++ b/tests/ui/let_underscore_must_use.stderr
@@ -1,5 +1,5 @@
 error: non-binding let on a result of a `#[must_use]` function
-  --> $DIR/let_underscore.rs:66:5
+  --> $DIR/let_underscore_must_use.rs:66:5
    |
 LL |     let _ = f();
    |     ^^^^^^^^^^^^
@@ -8,7 +8,7 @@ LL |     let _ = f();
    = help: consider explicitly using function result
 
 error: non-binding let on an expression with `#[must_use]` type
-  --> $DIR/let_underscore.rs:67:5
+  --> $DIR/let_underscore_must_use.rs:67:5
    |
 LL |     let _ = g();
    |     ^^^^^^^^^^^^
@@ -16,7 +16,7 @@ LL |     let _ = g();
    = help: consider explicitly using expression value
 
 error: non-binding let on a result of a `#[must_use]` function
-  --> $DIR/let_underscore.rs:69:5
+  --> $DIR/let_underscore_must_use.rs:69:5
    |
 LL |     let _ = l(0_u32);
    |     ^^^^^^^^^^^^^^^^^
@@ -24,7 +24,7 @@ LL |     let _ = l(0_u32);
    = help: consider explicitly using function result
 
 error: non-binding let on a result of a `#[must_use]` function
-  --> $DIR/let_underscore.rs:73:5
+  --> $DIR/let_underscore_must_use.rs:73:5
    |
 LL |     let _ = s.f();
    |     ^^^^^^^^^^^^^^
@@ -32,7 +32,7 @@ LL |     let _ = s.f();
    = help: consider explicitly using function result
 
 error: non-binding let on an expression with `#[must_use]` type
-  --> $DIR/let_underscore.rs:74:5
+  --> $DIR/let_underscore_must_use.rs:74:5
    |
 LL |     let _ = s.g();
    |     ^^^^^^^^^^^^^^
@@ -40,7 +40,7 @@ LL |     let _ = s.g();
    = help: consider explicitly using expression value
 
 error: non-binding let on a result of a `#[must_use]` function
-  --> $DIR/let_underscore.rs:77:5
+  --> $DIR/let_underscore_must_use.rs:77:5
    |
 LL |     let _ = S::h();
    |     ^^^^^^^^^^^^^^^
@@ -48,7 +48,7 @@ LL |     let _ = S::h();
    = help: consider explicitly using function result
 
 error: non-binding let on an expression with `#[must_use]` type
-  --> $DIR/let_underscore.rs:78:5
+  --> $DIR/let_underscore_must_use.rs:78:5
    |
 LL |     let _ = S::p();
    |     ^^^^^^^^^^^^^^^
@@ -56,7 +56,7 @@ LL |     let _ = S::p();
    = help: consider explicitly using expression value
 
 error: non-binding let on a result of a `#[must_use]` function
-  --> $DIR/let_underscore.rs:80:5
+  --> $DIR/let_underscore_must_use.rs:80:5
    |
 LL |     let _ = S::a();
    |     ^^^^^^^^^^^^^^^
@@ -64,7 +64,7 @@ LL |     let _ = S::a();
    = help: consider explicitly using function result
 
 error: non-binding let on an expression with `#[must_use]` type
-  --> $DIR/let_underscore.rs:82:5
+  --> $DIR/let_underscore_must_use.rs:82:5
    |
 LL |     let _ = if true { Ok(()) } else { Err(()) };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -72,7 +72,7 @@ LL |     let _ = if true { Ok(()) } else { Err(()) };
    = help: consider explicitly using expression value
 
 error: non-binding let on a result of a `#[must_use]` function
-  --> $DIR/let_underscore.rs:86:5
+  --> $DIR/let_underscore_must_use.rs:86:5
    |
 LL |     let _ = a.is_ok();
    |     ^^^^^^^^^^^^^^^^^^
@@ -80,7 +80,7 @@ LL |     let _ = a.is_ok();
    = help: consider explicitly using function result
 
 error: non-binding let on an expression with `#[must_use]` type
-  --> $DIR/let_underscore.rs:88:5
+  --> $DIR/let_underscore_must_use.rs:88:5
    |
 LL |     let _ = a.map(|_| ());
    |     ^^^^^^^^^^^^^^^^^^^^^^
@@ -88,37 +88,12 @@ LL |     let _ = a.map(|_| ());
    = help: consider explicitly using expression value
 
 error: non-binding let on an expression with `#[must_use]` type
-  --> $DIR/let_underscore.rs:90:5
+  --> $DIR/let_underscore_must_use.rs:90:5
    |
 LL |     let _ = a;
    |     ^^^^^^^^^^
    |
    = help: consider explicitly using expression value
 
-error: non-binding let on an a synchronization lock
-  --> $DIR/let_underscore.rs:95:5
-   |
-LL |     let _ = m.lock();
-   |     ^^^^^^^^^^^^^^^^^
-   |
-   = note: `#[deny(clippy::let_underscore_lock)]` on by default
-   = help: consider using an underscore-prefixed named binding
-
-error: non-binding let on an a synchronization lock
-  --> $DIR/let_underscore.rs:96:5
-   |
-LL |     let _ = rw.read();
-   |     ^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider using an underscore-prefixed named binding
-
-error: non-binding let on an a synchronization lock
-  --> $DIR/let_underscore.rs:97:5
-   |
-LL |     let _ = rw.write();
-   |     ^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider using an underscore-prefixed named binding
-
-error: aborting due to 15 previous errors
+error: aborting due to 12 previous errors