diff --git a/src/lib.rs b/src/lib.rs
index 3698875..09d4d07 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -267,10 +267,7 @@ mod aux {
             }
         };
 
-        for function in module
-            .get_functions()
-            .filter(|f| f.count_basic_blocks() > 0)
-        {
+        for function in module.get_functions() {
             for bb in function.get_basic_blocks() {
                 for instr in bb.get_instructions() {
                     let Ok(call) = CallSiteValue::try_from(instr) else {
@@ -793,20 +790,7 @@ mod aux {
         }
 
         let call_args: Vec<BasicValueEnum> = extract_operands(instr)?;
-        let qubit_ptr = match call_args.as_slice() {
-            [BasicValueEnum::PointerValue(ptr), _] => *ptr,
-            [_, _] => {
-                return Err(
-                    "Malformed mz_leaked call: expected first argument to be a pointer".into(),
-                );
-            }
-            _ => {
-                return Err(format!(
-                    "Malformed mz_leaked call: expected 1 argument plus callee, got {} operands",
-                    call_args.len()
-                ));
-            }
-        };
+        let qubit_ptr = mz_leaked_qubit_operand(&call_args)?;
 
         let q_handle = {
             let idx_fn = module
@@ -878,6 +862,21 @@ mod aux {
         Ok(())
     }
 
+    pub fn mz_leaked_qubit_operand<'ctx>(
+        call_args: &[BasicValueEnum<'ctx>],
+    ) -> Result<PointerValue<'ctx>, String> {
+        match call_args {
+            [BasicValueEnum::PointerValue(ptr), _] => Ok(*ptr),
+            [_, _] => {
+                Err("Malformed mz_leaked call: expected first argument to be a pointer".into())
+            }
+            _ => Err(format!(
+                "Malformed mz_leaked call: expected 1 argument plus callee, got {} operands",
+                call_args.len()
+            )),
+        }
+    }
+
     fn handle_reset_call(args: &ProcessCallArgs) -> Result<(), String> {
         let ProcessCallArgs {
             ctx, module, instr, ..
@@ -2997,6 +2996,56 @@ declare void @__quantum__rt__result_record_output(%Result*, i8*)
         assert!(err.contains("Malformed mz_leaked call: expected signature i64 (ptr)"));
     }
 
+    #[test]
+    fn test_qir_to_qis_rejects_mz_leaked_with_wrong_return_width() {
+        let ll_text = minimal_qir_with_body(
+            "1",
+            "0",
+            "1",
+            "declare i1 @__quantum__qis__mz_leaked__body(%Qubit*)",
+            r"  %0 = call i1 @__quantum__qis__mz_leaked__body(%Qubit* null)",
+        );
+
+        let bc_bytes = qir_ll_to_bc(&ll_text).expect("Failed to convert inline QIR to bitcode");
+        let err = qir_to_qis(&bc_bytes, 0, "native", None)
+            .expect_err("mz_leaked with the wrong return width should fail cleanly");
+        assert_eq!(
+            err,
+            "Malformed mz_leaked call: expected signature i64 (ptr)"
+        );
+    }
+
+    #[test]
+    fn test_qir_to_qis_rejects_mz_leaked_with_non_pointer_parameter() {
+        let ll_text = minimal_qir_with_body(
+            "1",
+            "0",
+            "1",
+            "declare i64 @__quantum__qis__mz_leaked__body(i64)",
+            r"  %0 = call i64 @__quantum__qis__mz_leaked__body(i64 0)",
+        );
+
+        let bc_bytes = qir_ll_to_bc(&ll_text).expect("Failed to convert inline QIR to bitcode");
+        let err = qir_to_qis(&bc_bytes, 0, "native", None)
+            .expect_err("mz_leaked with a non-pointer parameter should fail cleanly");
+        assert_eq!(
+            err,
+            "Malformed mz_leaked call: expected signature i64 (ptr)"
+        );
+    }
+
+    #[test]
+    fn test_mz_leaked_operand_check_rejects_non_pointer_first_operand() {
+        let ctx = Context::create();
+        let value = ctx.i64_type().const_zero().into();
+        let err = crate::aux::mz_leaked_qubit_operand(&[value, value])
+            .expect_err("non-pointer mz_leaked operands should fail cleanly");
+        assert_eq!(
+            err,
+            "Malformed mz_leaked call: expected first argument to be a pointer"
+        );
+    }
+
     #[cfg(not(windows))]
     #[test]
     fn test_qir_to_qis_mz_leaked_lowers_via_uint_future_runtime() {