diff --git a/src/librustc_mir/interpret/validity.rs b/src/librustc_mir/interpret/validity.rs
index 8b97d9ded7449..6b932b17524c9 100644
--- a/src/librustc_mir/interpret/validity.rs
+++ b/src/librustc_mir/interpret/validity.rs
@@ -357,8 +357,10 @@ impl<'rt, 'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>>
                         match err.kind {
                             EvalErrorKind::InvalidNullPointerUsage =>
                                 return validation_failure!("NULL reference", self.path),
-                            EvalErrorKind::AlignmentCheckFailed { .. } =>
-                                return validation_failure!("unaligned reference", self.path),
+                            EvalErrorKind::AlignmentCheckFailed { required, has } =>
+                                return validation_failure!(format!("unaligned reference \
+                                    (required {} byte alignment but found {})",
+                                    required.bytes(), has.bytes()), self.path),
                             _ =>
                                 return validation_failure!(
                                     "dangling (out-of-bounds) reference (might be NULL at \
diff --git a/src/test/ui/consts/const-eval/ub-ref.rs b/src/test/ui/consts/const-eval/ub-ref.rs
index 3b19f3b07753e..0d8f30159b316 100644
--- a/src/test/ui/consts/const-eval/ub-ref.rs
+++ b/src/test/ui/consts/const-eval/ub-ref.rs
@@ -1,3 +1,4 @@
+// ignore-tidy-linelength
 #![feature(const_transmute)]
 #![allow(const_err)] // make sure we cannot allow away the errors tested here
 
@@ -5,6 +6,7 @@ use std::mem;
 
 const UNALIGNED: &u16 = unsafe { mem::transmute(&[0u8; 4]) };
 //~^ ERROR it is undefined behavior to use this value
+//~^^ type validation failed: encountered unaligned reference (required 2 byte alignment but found 1)
 
 const NULL: &u16 = unsafe { mem::transmute(0usize) };
 //~^ ERROR it is undefined behavior to use this value
diff --git a/src/test/ui/consts/const-eval/ub-ref.stderr b/src/test/ui/consts/const-eval/ub-ref.stderr
index f8b5b2f50ce04..33535c235e3a3 100644
--- a/src/test/ui/consts/const-eval/ub-ref.stderr
+++ b/src/test/ui/consts/const-eval/ub-ref.stderr
@@ -1,13 +1,13 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:6:1
+  --> $DIR/ub-ref.rs:7:1
    |
 LL | const UNALIGNED: &u16 = unsafe { mem::transmute(&[0u8; 4]) };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered unaligned reference
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered unaligned reference (required 2 byte alignment but found 1)
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:9:1
+  --> $DIR/ub-ref.rs:11:1
    |
 LL | const NULL: &u16 = unsafe { mem::transmute(0usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected something greater or equal to 1
@@ -15,7 +15,7 @@ LL | const NULL: &u16 = unsafe { mem::transmute(0usize) };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:12:1
+  --> $DIR/ub-ref.rs:14:1
    |
 LL | const REF_AS_USIZE: usize = unsafe { mem::transmute(&0) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected initialized plain (non-pointer) bytes
@@ -23,7 +23,7 @@ LL | const REF_AS_USIZE: usize = unsafe { mem::transmute(&0) };
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:15:1
+  --> $DIR/ub-ref.rs:17:1
    |
 LL | const REF_AS_USIZE_SLICE: &[usize] = &[unsafe { mem::transmute(&0) }];
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer at .<deref>, but expected plain (non-pointer) bytes
@@ -31,7 +31,7 @@ LL | const REF_AS_USIZE_SLICE: &[usize] = &[unsafe { mem::transmute(&0) }];
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-ref.rs:18:1
+  --> $DIR/ub-ref.rs:20:1
    |
 LL | const USIZE_AS_REF: &'static u8 = unsafe { mem::transmute(1337usize) };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered integer pointer in non-ZST reference