diff --git a/compiler/rustc_passes/src/eii.rs b/compiler/rustc_passes/src/eii.rs
index 691576e6a05fc..0e2d495924b67 100644
--- a/compiler/rustc_passes/src/eii.rs
+++ b/compiler/rustc_passes/src/eii.rs
@@ -116,7 +116,14 @@ pub(crate) fn check_externally_implementable_items<'tcx>(tcx: TyCtxt<'tcx>, ():
         }
 
         if default_impls.len() > 1 {
-            panic!("multiple not supported right now");
+            tcx.dcx().span_err(
+                decl.span,
+                format!(
+                    "`{}` has more than one default implementation which is not supported",
+                    tcx.item_name(decl_did)
+                ),
+            );
+            continue;
         }
 
         let (local_impl, is_default) =
diff --git a/e -i HEAD~2 b/e -i HEAD~2
new file mode 100644
index 0000000000000..c04fda91ad7d3
--- /dev/null
+++ b/e -i HEAD~2	
@@ -0,0 +1,10 @@
+49b9580aa04 (HEAD -> main, origin/main, origin/HEAD) fixed the diagnostic message and fluent message inconsistency
+22a10e199b8 lint: treat  binders in improper_ctypes instead of ICE
+ba86c0460b0 Auto merge of #149704 - matthiaskrgr:rollup-u4zhw99, r=matthiaskrgr
+da2544bfbe8 Auto merge of #149495 - scottmcm:assume-filter-count, r=Mark-Simulacrum
+60a4413ff0e Rollup merge of #149683 - korken89:fix-armv8r-tier, r=jieyouxu
+4c8c967225b Rollup merge of #149401 - celinval:smir-109-name, r=scottmcm
+8a6f82efac8 Rollup merge of #148814 - bend-n:stabilize_array_windows, r=scottmcm
+f278da83859 Rollup merge of #148487 - Qelxiros:148441-option-into-flat-iter, r=scottmcm
+865650a52f5 Rollup merge of #146826 - bluurryy:impl-allocator-for-mut-a, r=scottmcm
+fbab541a7ad Auto merge of #149701 - jhpratt:rollup-cnlzfbv, r=jhpratt
diff --git a/tests/ui/eii/multiple-default-impls.rs b/tests/ui/eii/multiple-default-impls.rs
new file mode 100644
index 0000000000000..bf9cbfc7cb449
--- /dev/null
+++ b/tests/ui/eii/multiple-default-impls.rs
@@ -0,0 +1,13 @@
+//@ check-fail
+
+#![feature(extern_item_impls)]
+
+#[eii(eii1)]
+//~^ ERROR `eii1` has more than one default implementation which is not supported
+fn a() {}
+
+#[eii(eii1)]
+//~^ ERROR the name `eii1` is defined multiple times
+//~| ERROR `#[eii1]` required, but not found
+fn main() {}
+//~^ ERROR the `main` function cannot be declared in an `extern` block
diff --git a/tests/ui/eii/multiple-default-impls.stderr b/tests/ui/eii/multiple-default-impls.stderr
new file mode 100644
index 0000000000000..010720d36445b
--- /dev/null
+++ b/tests/ui/eii/multiple-default-impls.stderr
@@ -0,0 +1,34 @@
+error[E0428]: the name `eii1` is defined multiple times
+  --> $DIR/multiple-default-impls.rs:9:1
+   |
+LL | #[eii(eii1)]
+   | ------------ previous definition of the macro `eii1` here
+...
+LL | #[eii(eii1)]
+   | ^^^^^^^^^^^^ `eii1` redefined here
+   |
+   = note: `eii1` must be defined only once in the macro namespace of this module
+
+error: the `main` function cannot be declared in an `extern` block
+  --> $DIR/multiple-default-impls.rs:12:1
+   |
+LL | fn main() {}
+   | ^^^^^^^^^
+
+error: `eii1` has more than one default implementation which is not supported
+  --> $DIR/multiple-default-impls.rs:5:1
+   |
+LL | #[eii(eii1)]
+   | ^^^^^^^^^^^^
+
+error: `#[eii1]` required, but not found
+  --> $DIR/multiple-default-impls.rs:9:1
+   |
+LL | #[eii(eii1)]
+   | ^^^^^^^^^^^^ expected because `#[eii1]` was declared here in crate `multiple_default_impls`
+   |
+   = help: expected at least one implementation in crate `multiple_default_impls` or any of its dependencies
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0428`.