diff --git a/tests/fail/dyn-call-trait-mismatch.rs b/tests/fail/dyn-call-trait-mismatch.rs
new file mode 100644
index 000000000000..0e7c3dbcc040
--- /dev/null
+++ b/tests/fail/dyn-call-trait-mismatch.rs
@@ -0,0 +1,16 @@
+trait T1 {
+    fn method1(self: Box<Self>);
+}
+trait T2 {
+    fn method2(self: Box<Self>);
+}
+
+impl T1 for i32 {
+    fn method1(self: Box<Self>) {}
+}
+
+fn main() {
+    let r = Box::new(0) as Box<dyn T1>;
+    let r2: Box<dyn T2> = unsafe { std::mem::transmute(r) };
+    r2.method2(); //~ERROR: call on a pointer whose vtable does not match its type
+}
diff --git a/tests/fail/dyn-call-trait-mismatch.stderr b/tests/fail/dyn-call-trait-mismatch.stderr
new file mode 100644
index 000000000000..2673a22a3df2
--- /dev/null
+++ b/tests/fail/dyn-call-trait-mismatch.stderr
@@ -0,0 +1,15 @@
+error: Undefined Behavior: `dyn` call on a pointer whose vtable does not match its type
+  --> $DIR/dyn-call-trait-mismatch.rs:LL:CC
+   |
+LL |     r2.method2();
+   |     ^^^^^^^^^^^^ `dyn` call on a pointer whose vtable does not match its type
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: backtrace:
+   = note: inside `main` at $DIR/dyn-call-trait-mismatch.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+
diff --git a/tests/fail/dyn-upcast-trait-mismatch.rs b/tests/fail/dyn-upcast-trait-mismatch.rs
new file mode 100644
index 000000000000..f53e9a03f4be
--- /dev/null
+++ b/tests/fail/dyn-upcast-trait-mismatch.rs
@@ -0,0 +1,58 @@
+#![feature(trait_upcasting)]
+#![allow(incomplete_features)]
+
+trait Foo: PartialEq<i32> + std::fmt::Debug + Send + Sync {
+    fn a(&self) -> i32 {
+        10
+    }
+
+    fn z(&self) -> i32 {
+        11
+    }
+
+    fn y(&self) -> i32 {
+        12
+    }
+}
+
+trait Bar: Foo {
+    fn b(&self) -> i32 {
+        20
+    }
+
+    fn w(&self) -> i32 {
+        21
+    }
+}
+
+trait Baz: Bar {
+    fn c(&self) -> i32 {
+        30
+    }
+}
+
+impl Foo for i32 {
+    fn a(&self) -> i32 {
+        100
+    }
+}
+
+impl Bar for i32 {
+    fn b(&self) -> i32 {
+        200
+    }
+}
+
+impl Baz for i32 {
+    fn c(&self) -> i32 {
+        300
+    }
+}
+
+fn main() {
+    let baz: &dyn Baz = &1;
+    // We already fail on the implicit upcast inserted here.
+    let baz_fake: &dyn Bar = unsafe { std::mem::transmute(baz) };
+    //~^ERROR: upcast on a pointer whose vtable does not match its type
+    let _err = baz_fake as &dyn Foo;
+}
diff --git a/tests/fail/dyn-upcast-trait-mismatch.stderr b/tests/fail/dyn-upcast-trait-mismatch.stderr
new file mode 100644
index 000000000000..0e5e22b9b4b9
--- /dev/null
+++ b/tests/fail/dyn-upcast-trait-mismatch.stderr
@@ -0,0 +1,15 @@
+error: Undefined Behavior: upcast on a pointer whose vtable does not match its type
+  --> $DIR/dyn-upcast-trait-mismatch.rs:LL:CC
+   |
+LL |     let baz_fake: &dyn Bar = unsafe { std::mem::transmute(baz) };
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^ upcast on a pointer whose vtable does not match its type
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: backtrace:
+   = note: inside `main` at $DIR/dyn-upcast-trait-mismatch.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+