diff --git a/compiler/rustc_mir_transform/src/known_panics_lint.rs b/compiler/rustc_mir_transform/src/known_panics_lint.rs
index 38fc37a3a3131..baa25a10a6e89 100644
--- a/compiler/rustc_mir_transform/src/known_panics_lint.rs
+++ b/compiler/rustc_mir_transform/src/known_panics_lint.rs
@@ -102,8 +102,14 @@ impl<'tcx> Value<'tcx> {
                 }
                 (PlaceElem::Index(idx), Value::Aggregate { fields, .. }) => {
                     let idx = prop.get_const(idx.into())?.immediate()?;
-                    let idx = prop.ecx.read_target_usize(idx).ok()?;
-                    fields.get(FieldIdx::from_u32(idx.try_into().ok()?)).unwrap_or(&Value::Uninit)
+                    let idx: u32 = prop.ecx.read_target_usize(idx).ok()?.try_into().ok()?;
+
+                    let max: u32 = FieldIdx::MAX.index().try_into().ok()?;
+                    if idx > max {
+                        return None;
+                    }
+
+                    fields.get(FieldIdx::from_u32(idx)).unwrap_or(&Value::Uninit)
                 }
                 (
                     PlaceElem::ConstantIndex { offset, min_length: _, from_end: false },
diff --git a/tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.rs b/tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.rs
new file mode 100644
index 0000000000000..7750993f1e20a
--- /dev/null
+++ b/tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.rs
@@ -0,0 +1,13 @@
+// Regression test for #121126. Compiler was panicking when indexing an array
+// with an index that is out of bounds and its value is greater than the max
+// value allowed for an index.
+
+//@ build-fail
+
+fn main() {
+    [0][0xFFFF_FF01];
+//~^ ERROR this operation will panic at runtime [unconditional_panic]
+}
+
+// NOTE: In order for the test to be valid, the index can take on any value
+// between FieldIdx::MAX + 1 (= 0xFFF_FF01) and u32::MAX (= 0xFFF_FFFF)
diff --git a/tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.stderr b/tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.stderr
new file mode 100644
index 0000000000000..e530a994b14c3
--- /dev/null
+++ b/tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.stderr
@@ -0,0 +1,10 @@
+error: this operation will panic at runtime
+  --> $DIR/issue-121126-index-out-of-bounds-exceeds-max-value.rs:8:5
+   |
+LL |     [0][0xFFFF_FF01];
+   |     ^^^^^^^^^^^^^^^^ index out of bounds: the length is 1 but the index is 4294967041
+   |
+   = note: `#[deny(unconditional_panic)]` on by default
+
+error: aborting due to 1 previous error
+