diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index 6e2143858de8c..999d733e3a7c9 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -4,7 +4,7 @@ use rustc_abi::{Align, ExternAbi};
 use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, DiffActivity, DiffMode};
 use rustc_ast::{LitKind, MetaItem, MetaItemInner, attr};
 use rustc_attr_data_structures::{
-    AttributeKind, InlineAttr, InstructionSetAttr, OptimizeAttr, ReprAttr, UsedBy, find_attr,
+    AttributeKind, InlineAttr, InstructionSetAttr, OptimizeAttr, UsedBy, find_attr,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
@@ -109,14 +109,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
 
         if let hir::Attribute::Parsed(p) = attr {
             match p {
-                AttributeKind::Repr(reprs) => {
-                    codegen_fn_attrs.alignment = reprs
-                        .iter()
-                        .filter_map(
-                            |(r, _)| if let ReprAttr::ReprAlign(x) = r { Some(*x) } else { None },
-                        )
-                        .max();
-                }
                 AttributeKind::Cold(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD,
                 AttributeKind::ExportName { name, .. } => {
                     codegen_fn_attrs.export_name = Some(*name);
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
index 9a60c1510349a..74a9611d426ce 100644
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@@ -13,6 +13,10 @@ passes_abi_ne =
 passes_abi_of =
     fn_abi_of({$fn_name}) = {$fn_abi}
 
+passes_align_attr_application =
+    `#[align(...)]` should be applied to a function item
+    .label = not a function item
+
 passes_align_should_be_repr_align =
     `#[align(...)]` is not supported on {$item} items
     .suggestion = use `#[repr(align(...))]` instead
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 4bc48cb6aca6f..b2c6f21cd8845 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -1887,7 +1887,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     /// Checks if the `#[align]` attributes on `item` are valid.
     fn check_align(&self, span: Span, target: Target, align: Align, repr_span: Span) {
         match target {
-            Target::Fn | Target::Method(_) => {}
+            Target::Fn | Target::Method(_) | Target::ForeignFn => {}
             Target::Struct | Target::Union | Target::Enum => {
                 self.dcx().emit_err(errors::AlignShouldBeReprAlign {
                     span: repr_span,
@@ -1896,10 +1896,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 });
             }
             _ => {
-                self.dcx().emit_err(errors::AttrApplication::StructEnumUnion {
-                    hint_span: repr_span,
-                    span,
-                });
+                self.dcx().emit_err(errors::AlignAttrApplication { hint_span: repr_span, span });
             }
         }
 
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index d498827707332..76608c2795dce 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -1838,3 +1838,12 @@ pub(crate) struct AlignShouldBeReprAlign {
     pub item: &'static str,
     pub align_bytes: u64,
 }
+
+#[derive(Diagnostic)]
+#[diag(passes_align_attr_application)]
+pub(crate) struct AlignAttrApplication {
+    #[primary_span]
+    pub hint_span: Span,
+    #[label]
+    pub span: Span,
+}
diff --git a/tests/codegen/align-fn.rs b/tests/codegen/align-fn.rs
index 90073ff308143..c871d1259507f 100644
--- a/tests/codegen/align-fn.rs
+++ b/tests/codegen/align-fn.rs
@@ -1,4 +1,5 @@
 //@ compile-flags: -C no-prepopulate-passes -Z mir-opt-level=0 -Clink-dead-code
+//@ edition: 2024
 
 #![crate_type = "lib"]
 #![feature(fn_align)]
@@ -116,3 +117,24 @@ pub fn align_specified_twice_2() {}
 #[align(32)]
 #[align(256)]
 pub fn align_specified_twice_3() {}
+
+const _: () = {
+    // CHECK-LABEL: align_unmangled
+    // CHECK-SAME: align 256
+    #[unsafe(no_mangle)]
+    #[align(32)]
+    #[align(256)]
+    extern "C" fn align_unmangled() {}
+};
+
+unsafe extern "C" {
+    #[align(256)]
+    fn align_unmangled();
+}
+
+// FIXME also check `gen` et al
+// CHECK-LABEL: async_align
+// CHECK-SAME: align 64
+#[unsafe(no_mangle)]
+#[align(64)]
+pub async fn async_align() {}
diff --git a/tests/ui/attributes/fn-align-dyn.rs b/tests/ui/attributes/fn-align-dyn.rs
new file mode 100644
index 0000000000000..d67de05e7a9fd
--- /dev/null
+++ b/tests/ui/attributes/fn-align-dyn.rs
@@ -0,0 +1,15 @@
+//@ run-pass
+#![feature(fn_align)]
+
+trait Test {
+    #[align(4096)]
+    fn foo(&self);
+
+    #[align(4096)]
+    fn foo1(&self);
+}
+
+fn main() {
+    assert_eq!((<dyn Test>::foo as fn(_) as usize & !1) % 4096, 0);
+    assert_eq!((<dyn Test>::foo1 as fn(_) as usize & !1) % 4096, 0);
+}
diff --git a/tests/ui/attributes/malformed-fn-align.rs b/tests/ui/attributes/malformed-fn-align.rs
index f5ab9555e561f..e06e611684242 100644
--- a/tests/ui/attributes/malformed-fn-align.rs
+++ b/tests/ui/attributes/malformed-fn-align.rs
@@ -21,5 +21,29 @@ fn f3() {}
 #[repr(align(16))] //~ ERROR `#[repr(align(...))]` is not supported on function items
 fn f4() {}
 
+#[align(-1)] //~ ERROR expected unsuffixed literal, found `-`
+fn f5() {}
+
+#[align(3)] //~ ERROR invalid alignment value: not a power of two
+fn f6() {}
+
+#[align(4usize)] //~ ERROR invalid alignment value: not an unsuffixed integer [E0589]
+//~^ ERROR suffixed literals are not allowed in attributes
+fn f7() {}
+
+#[align(16)]
+#[align(3)] //~ ERROR invalid alignment value: not a power of two
+#[align(16)]
+fn f8() {}
+
 #[align(16)] //~ ERROR `#[align(...)]` is not supported on struct items
 struct S1;
+
+#[align(32)] //~ ERROR `#[align(...)]` should be applied to a function item
+const FOO: i32 = 42;
+
+#[align(32)] //~ ERROR `#[align(...)]` should be applied to a function item
+mod test {}
+
+#[align(32)] //~ ERROR `#[align(...)]` should be applied to a function item
+use ::std::iter;
diff --git a/tests/ui/attributes/malformed-fn-align.stderr b/tests/ui/attributes/malformed-fn-align.stderr
index b769d0b457ddd..af3625b1f3b9e 100644
--- a/tests/ui/attributes/malformed-fn-align.stderr
+++ b/tests/ui/attributes/malformed-fn-align.stderr
@@ -1,3 +1,17 @@
+error: expected unsuffixed literal, found `-`
+  --> $DIR/malformed-fn-align.rs:24:9
+   |
+LL | #[align(-1)]
+   |         ^
+
+error: suffixed literals are not allowed in attributes
+  --> $DIR/malformed-fn-align.rs:30:9
+   |
+LL | #[align(4usize)]
+   |         ^^^^^^
+   |
+   = help: instead of using a suffixed literal (`1u8`, `1.0f32`, etc.), use an unsuffixed version (`1`, `1.0`, etc.)
+
 error[E0539]: malformed `align` attribute input
   --> $DIR/malformed-fn-align.rs:5:5
    |
@@ -37,6 +51,24 @@ error[E0589]: invalid alignment value: not a power of two
 LL | #[align(0)]
    |         ^
 
+error[E0589]: invalid alignment value: not a power of two
+  --> $DIR/malformed-fn-align.rs:27:9
+   |
+LL | #[align(3)]
+   |         ^
+
+error[E0589]: invalid alignment value: not an unsuffixed integer
+  --> $DIR/malformed-fn-align.rs:30:9
+   |
+LL | #[align(4usize)]
+   |         ^^^^^^
+
+error[E0589]: invalid alignment value: not a power of two
+  --> $DIR/malformed-fn-align.rs:35:9
+   |
+LL | #[align(3)]
+   |         ^
+
 error: `#[repr(align(...))]` is not supported on function items
   --> $DIR/malformed-fn-align.rs:21:8
    |
@@ -50,7 +82,7 @@ LL | #[repr(align(16))]
    |        ^^^^^^^^^
 
 error: `#[align(...)]` is not supported on struct items
-  --> $DIR/malformed-fn-align.rs:24:1
+  --> $DIR/malformed-fn-align.rs:39:1
    |
 LL | #[align(16)]
    | ^^^^^^^^^^^^
@@ -61,7 +93,31 @@ LL - #[align(16)]
 LL + #[repr(align(16))]
    |
 
-error: aborting due to 7 previous errors
+error: `#[align(...)]` should be applied to a function item
+  --> $DIR/malformed-fn-align.rs:42:1
+   |
+LL | #[align(32)]
+   | ^^^^^^^^^^^^
+LL | const FOO: i32 = 42;
+   | -------------------- not a function item
+
+error: `#[align(...)]` should be applied to a function item
+  --> $DIR/malformed-fn-align.rs:45:1
+   |
+LL | #[align(32)]
+   | ^^^^^^^^^^^^
+LL | mod test {}
+   | ----------- not a function item
+
+error: `#[align(...)]` should be applied to a function item
+  --> $DIR/malformed-fn-align.rs:48:1
+   |
+LL | #[align(32)]
+   | ^^^^^^^^^^^^
+LL | use ::std::iter;
+   | ---------------- not a function item
+
+error: aborting due to 15 previous errors
 
 Some errors have detailed explanations: E0539, E0589, E0805.
 For more information about an error, try `rustc --explain E0539`.