3 files changed, 31 insertions, 1 deletions
diff --git a/tests/ui/mut_mutex_lock.fixed b/tests/ui/mut_mutex_lock.fixed
index bbedbb2bed2..29c5a27cb62 100644
--- a/tests/ui/mut_mutex_lock.fixed
+++ b/tests/ui/mut_mutex_lock.fixed
@@ -9,6 +9,11 @@ fn mut_mutex_lock() {
 
     let mut value = value_mutex.get_mut().unwrap();
     *value += 1;
+
+    let mut value_mutex = Mutex::new(42_u8);
+    let mut_ref_mut_ref_mutex = &mut &mut value_mutex;
+    let mut value = mut_ref_mut_ref_mutex.get_mut().unwrap();
+    *value += 1;
 }
 
 fn no_owned_mutex_lock() {
@@ -24,4 +29,11 @@ fn issue9415() {
     *guard += 1;
 }
 
+fn mut_ref_ref_mutex_lock() {
+    let mutex = Mutex::new(42_u8);
+    let mut_ref_ref_mutex = &mut &mutex;
+    let mut guard = mut_ref_ref_mutex.lock().unwrap();
+    *guard += 1;
+}
+
 fn main() {}
diff --git a/tests/ui/mut_mutex_lock.rs b/tests/ui/mut_mutex_lock.rs
index 74116100e82..fcdb3ff97db 100644
--- a/tests/ui/mut_mutex_lock.rs
+++ b/tests/ui/mut_mutex_lock.rs
@@ -9,6 +9,11 @@ fn mut_mutex_lock() {
 
     let mut value = value_mutex.lock().unwrap();
     *value += 1;
+
+    let mut value_mutex = Mutex::new(42_u8);
+    let mut_ref_mut_ref_mutex = &mut &mut value_mutex;
+    let mut value = mut_ref_mut_ref_mutex.lock().unwrap();
+    *value += 1;
 }
 
 fn no_owned_mutex_lock() {
@@ -24,4 +29,11 @@ fn issue9415() {
     *guard += 1;
 }
 
+fn mut_ref_ref_mutex_lock() {
+    let mutex = Mutex::new(42_u8);
+    let mut_ref_ref_mutex = &mut &mutex;
+    let mut guard = mut_ref_ref_mutex.lock().unwrap();
+    *guard += 1;
+}
+
 fn main() {}
diff --git a/tests/ui/mut_mutex_lock.stderr b/tests/ui/mut_mutex_lock.stderr
index a3d4905c04c..92601c4c612 100644
--- a/tests/ui/mut_mutex_lock.stderr
+++ b/tests/ui/mut_mutex_lock.stderr
@@ -7,5 +7,11 @@ LL |     let mut value = value_mutex.lock().unwrap();
    = note: `-D clippy::mut-mutex-lock` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::mut_mutex_lock)]`
 
-error: aborting due to 1 previous error
+error: calling `&mut Mutex::lock` unnecessarily locks an exclusive (mutable) reference
+  --> tests/ui/mut_mutex_lock.rs:15:43
+   |
+LL |     let mut value = mut_ref_mut_ref_mutex.lock().unwrap();
+   |                                           ^^^^ help: change this to: `get_mut`
+
+error: aborting due to 2 previous errors