diff --git a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.rs b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.rs
index 53e98d2eb1bc..2e73ef8c32f5 100644
--- a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.rs
+++ b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.rs
@@ -24,3 +24,24 @@ pub extern "cmse-nonsecure-entry" fn f4(_: AlignRelevant, _: u32) {} //~ ERROR [
 #[no_mangle]
 #[allow(improper_ctypes_definitions)]
 pub extern "cmse-nonsecure-entry" fn f5(_: [u32; 5]) {} //~ ERROR [E0798]
+
+struct Four {
+    a: u32,
+    b: u32,
+    c: u32,
+    d: u32,
+}
+
+struct Five {
+    a: u32,
+    b: u32,
+    c: u32,
+    d: u32,
+    e: u32,
+}
+
+#[no_mangle]
+pub extern "cmse-nonsecure-entry" fn four(_: Four) {}
+
+#[no_mangle]
+pub extern "cmse-nonsecure-entry" fn five(_: Five) {} //~ ERROR [E0798]
diff --git a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.stderr b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.stderr
index af8277d314ba..c17cf50a6139 100644
--- a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.stderr
+++ b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/params-via-stack.stderr
@@ -40,6 +40,14 @@ LL | pub extern "cmse-nonsecure-entry" fn f5(_: [u32; 5]) {}
    |
    = note: functions with the `"cmse-nonsecure-entry"` ABI must pass all their arguments via the 4 32-bit argument registers
 
-error: aborting due to 5 previous errors
+error[E0798]: arguments for `"cmse-nonsecure-entry"` function too large to pass via registers
+  --> $DIR/params-via-stack.rs:47:46
+   |
+LL | pub extern "cmse-nonsecure-entry" fn five(_: Five) {}
+   |                                              ^^^^ does not fit in the available registers
+   |
+   = note: functions with the `"cmse-nonsecure-entry"` ABI must pass all their arguments via the 4 32-bit argument registers
+
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0798`.
diff --git a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/via-registers.rs b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/via-registers.rs
index 0a6565e37fc7..756cc6816acd 100644
--- a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/via-registers.rs
+++ b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/via-registers.rs
@@ -40,9 +40,15 @@ pub extern "cmse-nonsecure-entry" fn inputs5(_: f64, _: f32, _: f32) {}
 #[no_mangle]
 pub extern "cmse-nonsecure-entry" fn inputs6(_: ReprTransparentStruct<u64>, _: U32Compound) {}
 #[no_mangle]
-#[allow(improper_ctypes_definitions)]
+#[expect(improper_ctypes_definitions)]
 pub extern "cmse-nonsecure-entry" fn inputs7(_: [u32; 4]) {}
 
+// With zero-sized types we can actually have more than 4 arguments.
+#[expect(improper_ctypes_definitions)]
+pub extern "cmse-nonsecure-entry" fn inputs8(_: (), _: (), _: (), _: (), _: ()) {}
+#[expect(improper_ctypes_definitions)]
+pub extern "cmse-nonsecure-entry" fn inputs9(_: (), _: (), _: (), _: (), _: ()) {}
+
 #[no_mangle]
 pub extern "cmse-nonsecure-entry" fn outputs1() -> u32 {
     0
@@ -69,8 +75,8 @@ pub extern "cmse-nonsecure-entry" fn outputs6() -> ReprTransparentStruct<u64> {
     ReprTransparentStruct { _marker1: (), _marker2: (), field: 0xAA, _marker3: () }
 }
 #[no_mangle]
-pub extern "cmse-nonsecure-entry" fn outputs7(
-) -> ReprTransparentStruct<ReprTransparentStruct<u64>> {
+pub extern "cmse-nonsecure-entry" fn outputs7() -> ReprTransparentStruct<ReprTransparentStruct<u64>>
+{
     ReprTransparentStruct {
         _marker1: (),
         _marker2: (),