diff --git a/src/librustc_mir/interpret/memory.rs b/src/librustc_mir/interpret/memory.rs
index 222bef4ff136b..4b0c0c3ee6173 100644
--- a/src/librustc_mir/interpret/memory.rs
+++ b/src/librustc_mir/interpret/memory.rs
@@ -846,7 +846,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
         &self,
         ptr: Scalar<M::PointerTag>,
         size: Size,
-        allow_ptr: bool,
+        allow_ptr_and_undef: bool,
     ) -> EvalResult<'tcx> {
         // Empty accesses don't need to be valid pointers, but they should still be non-NULL
         let align = Align::from_bytes(1, 1).unwrap();
@@ -857,9 +857,9 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> Memory<'a, 'mir, 'tcx, M> {
         let ptr = ptr.to_ptr()?;
         // Check bounds, align and relocations on the edges
         self.get_bytes_with_undef_and_ptr(ptr, size, align)?;
-        // Check undef, and maybe ptr
-        self.check_defined(ptr, size)?;
-        if !allow_ptr {
+        // Check undef and ptr
+        if !allow_ptr_and_undef {
+            self.check_defined(ptr, size)?;
             self.check_relocations(ptr, size)?;
         }
         Ok(())
diff --git a/src/librustc_mir/interpret/validity.rs b/src/librustc_mir/interpret/validity.rs
index aadb5cc871e1a..c446980d04995 100644
--- a/src/librustc_mir/interpret/validity.rs
+++ b/src/librustc_mir/interpret/validity.rs
@@ -517,7 +517,12 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
                         // reject it.  However, that's good: We don't inherently want
                         // to reject those pointers, we just do not have the machinery to
                         // talk about parts of a pointer.
-                        match self.memory.check_bytes(dest.ptr, size, /*allow_ptr*/!const_mode) {
+                        // We also accept undef, for consistency with the type-based checks.
+                        match self.memory.check_bytes(
+                            dest.ptr,
+                            size,
+                            /*allow_ptr_and_undef*/!const_mode,
+                        ) {
                             // In the happy case, we needn't check anything else.
                             Ok(()) => {},
                             // Some error happened, try to provide a more detailed description.