diff --git a/src/librustc_mir/hair/pattern/_match.rs b/src/librustc_mir/hair/pattern/_match.rs
index 15f88334e8d5..8d7e605f7c9a 100644
--- a/src/librustc_mir/hair/pattern/_match.rs
+++ b/src/librustc_mir/hair/pattern/_match.rs
@@ -2042,7 +2042,7 @@ fn split_grouped_constructors<'p, 'tcx>(
                 //
                 // Of course, if fixed-length patterns exist, we must be sure
                 // that our length is large enough to miss them all, so
-                // we can pick `L = max(FIXED_LEN+1 ∪ {max(PREFIX_LEN) + max(SUFFIX_LEN)})`
+                // we can pick `L = max(max(FIXED_LEN)+1, max(PREFIX_LEN) + max(SUFFIX_LEN))`
                 //
                 // for example, with the above pair of patterns, all elements
                 // but the first and last can be added/removed, so any
@@ -2080,9 +2080,24 @@ fn split_grouped_constructors<'p, 'tcx>(
                     }
                 }
 
-                let max_slice_length = cmp::max(max_fixed_len + 1, max_prefix_len + max_suffix_len);
-                split_ctors
-                    .extend((self_prefix + self_suffix..=max_slice_length).map(FixedLenSlice))
+                // For diagnostics, we keep the prefix and suffix lengths separate, so in the case
+                // where `max_fixed_len+1` is the largest, we adapt `max_prefix_len` accordingly,
+                // so that `L = max_prefix_len + max_suffix_len`.
+                if max_fixed_len + 1 >= max_prefix_len + max_suffix_len {
+                    // The subtraction can't overflow thanks to the above check.
+                    // The new `max_prefix_len` is also guaranteed to be larger than its previous
+                    // value.
+                    max_prefix_len = max_fixed_len + 1 - max_suffix_len;
+                }
+
+                // `ctor` originally covered the range `(self_prefix + self_suffix..infinity)`. We
+                // now split it into two: lengths smaller than `max_prefix_len + max_suffix_len`
+                // are treated independently as fixed-lengths slices, and lengths above are
+                // captured by a final VarLenSlice constructor.
+                split_ctors.extend(
+                    (self_prefix + self_suffix..max_prefix_len + max_suffix_len).map(FixedLenSlice),
+                );
+                split_ctors.push(VarLenSlice(max_prefix_len, max_suffix_len));
             }
             // Any other constructor can be used unchanged.
             _ => split_ctors.push(ctor),
diff --git a/src/test/ui/pattern/usefulness/match-slice-patterns.rs b/src/test/ui/pattern/usefulness/match-slice-patterns.rs
index afbeb61e4415..af7fd53a1f1e 100644
--- a/src/test/ui/pattern/usefulness/match-slice-patterns.rs
+++ b/src/test/ui/pattern/usefulness/match-slice-patterns.rs
@@ -2,7 +2,7 @@
 
 fn check(list: &[Option<()>]) {
     match list {
-    //~^ ERROR `&[_, Some(_), None, _]` not covered
+    //~^ ERROR `&[_, Some(_), .., None, _]` not covered
         &[] => {},
         &[_] => {},
         &[_, _] => {},
diff --git a/src/test/ui/pattern/usefulness/match-slice-patterns.stderr b/src/test/ui/pattern/usefulness/match-slice-patterns.stderr
index 24769db34c93..72ae5d5fe3b3 100644
--- a/src/test/ui/pattern/usefulness/match-slice-patterns.stderr
+++ b/src/test/ui/pattern/usefulness/match-slice-patterns.stderr
@@ -1,8 +1,8 @@
-error[E0004]: non-exhaustive patterns: `&[_, Some(_), None, _]` not covered
+error[E0004]: non-exhaustive patterns: `&[_, Some(_), .., None, _]` not covered
   --> $DIR/match-slice-patterns.rs:4:11
    |
 LL |     match list {
-   |           ^^^^ pattern `&[_, Some(_), None, _]` not covered
+   |           ^^^^ pattern `&[_, Some(_), .., None, _]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
diff --git a/src/test/ui/pattern/usefulness/slice-patterns.rs b/src/test/ui/pattern/usefulness/slice-patterns.rs
index e11f11ba7524..da2d40caf1a4 100644
--- a/src/test/ui/pattern/usefulness/slice-patterns.rs
+++ b/src/test/ui/pattern/usefulness/slice-patterns.rs
@@ -37,7 +37,7 @@ fn main() {
         [.., false] => {}
     }
     match s {
-    //~^ ERROR `&[false, true]` not covered
+    //~^ ERROR `&[false, .., true]` not covered
         [] => {}
         [true, ..] => {}
         [.., false] => {}
@@ -57,18 +57,18 @@ fn main() {
         [_] => {}
     }
     match s {
-    //~^ ERROR `&[false]` not covered
+    //~^ ERROR `&[false, ..]` not covered
         [] => {}
         [true, ..] => {}
     }
     match s {
-    //~^ ERROR `&[false, _]` not covered
+    //~^ ERROR `&[false, _, ..]` not covered
         [] => {}
         [_] => {}
         [true, ..] => {}
     }
     match s {
-    //~^ ERROR `&[_, false]` not covered
+    //~^ ERROR `&[_, .., false]` not covered
         [] => {}
         [_] => {}
         [.., true] => {}
@@ -94,14 +94,14 @@ fn main() {
         [..] => {}
     }
     match s {
-    //~^ ERROR `&[_, _, true]` not covered
+    //~^ ERROR `&[_, _, .., true]` not covered
         [] => {}
         [_] => {}
         [_, _] => {}
         [.., false] => {}
     }
     match s {
-    //~^ ERROR `&[true, _, _]` not covered
+    //~^ ERROR `&[true, _, .., _]` not covered
         [] => {}
         [_] => {}
         [_, _] => {}
diff --git a/src/test/ui/pattern/usefulness/slice-patterns.stderr b/src/test/ui/pattern/usefulness/slice-patterns.stderr
index 666e16627c57..6afe4705b0e6 100644
--- a/src/test/ui/pattern/usefulness/slice-patterns.stderr
+++ b/src/test/ui/pattern/usefulness/slice-patterns.stderr
@@ -14,11 +14,11 @@ LL |     match s3 {
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[false, true]` not covered
+error[E0004]: non-exhaustive patterns: `&[false, .., true]` not covered
   --> $DIR/slice-patterns.rs:39:11
    |
 LL |     match s {
-   |           ^ pattern `&[false, true]` not covered
+   |           ^ pattern `&[false, .., true]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
@@ -46,27 +46,27 @@ LL |     match s {
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[false]` not covered
+error[E0004]: non-exhaustive patterns: `&[false, ..]` not covered
   --> $DIR/slice-patterns.rs:59:11
    |
 LL |     match s {
-   |           ^ pattern `&[false]` not covered
+   |           ^ pattern `&[false, ..]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[false, _]` not covered
+error[E0004]: non-exhaustive patterns: `&[false, _, ..]` not covered
   --> $DIR/slice-patterns.rs:64:11
    |
 LL |     match s {
-   |           ^ pattern `&[false, _]` not covered
+   |           ^ pattern `&[false, _, ..]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[_, false]` not covered
+error[E0004]: non-exhaustive patterns: `&[_, .., false]` not covered
   --> $DIR/slice-patterns.rs:70:11
    |
 LL |     match s {
-   |           ^ pattern `&[_, false]` not covered
+   |           ^ pattern `&[_, .., false]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
@@ -112,19 +112,19 @@ error: unreachable pattern
 LL |         [false, true] => {}
    |         ^^^^^^^^^^^^^
 
-error[E0004]: non-exhaustive patterns: `&[_, _, true]` not covered
+error[E0004]: non-exhaustive patterns: `&[_, _, .., true]` not covered
   --> $DIR/slice-patterns.rs:96:11
    |
 LL |     match s {
-   |           ^ pattern `&[_, _, true]` not covered
+   |           ^ pattern `&[_, _, .., true]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[true, _, _]` not covered
+error[E0004]: non-exhaustive patterns: `&[true, _, .., _]` not covered
   --> $DIR/slice-patterns.rs:103:11
    |
 LL |     match s {
-   |           ^ pattern `&[true, _, _]` not covered
+   |           ^ pattern `&[true, _, .., _]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms