diff --git a/crates/lean_compiler/src/a_simplify_lang.rs b/crates/lean_compiler/src/a_simplify_lang.rs
index 4c86348d..f985a3cd 100644
--- a/crates/lean_compiler/src/a_simplify_lang.rs
+++ b/crates/lean_compiler/src/a_simplify_lang.rs
@@ -160,6 +160,8 @@ pub fn simplify_program(mut program: Program) -> SimpleProgram {
     for (name, func) in &program.functions {
         let mut array_manager = ArrayManager::default();
         let simplified_instructions = simplify_lines(
+            &program.functions,
+            func.n_returned_vars,
             &func.body,
             &mut counters,
             &mut new_functions,
@@ -435,7 +437,10 @@ impl ArrayManager {
     }
 }
 
+#[allow(clippy::too_many_arguments)]
 fn simplify_lines(
+    functions: &BTreeMap<String, Function>,
+    n_returned_vars: usize,
     lines: &[Line],
     counters: &mut Counters,
     new_functions: &mut BTreeMap<String, SimpleFunction>,
@@ -455,6 +460,8 @@ fn simplify_lines(
                 for (i, (pattern, statements)) in arms.iter().enumerate() {
                     assert_eq!(*pattern, i, "match patterns should be consecutive, starting from 0");
                     simple_arms.push(simplify_lines(
+                        functions,
+                        n_returned_vars,
                         statements,
                         counters,
                         new_functions,
@@ -606,6 +613,8 @@ fn simplify_lines(
 
                 let mut array_manager_then = array_manager.clone();
                 let then_branch_simplified = simplify_lines(
+                    functions,
+                    n_returned_vars,
                     then_branch,
                     counters,
                     new_functions,
@@ -617,6 +626,8 @@ fn simplify_lines(
                 array_manager_else.valid = array_manager.valid.clone(); // Crucial: remove the access added in the IF branch
 
                 let else_branch_simplified = simplify_lines(
+                    functions,
+                    n_returned_vars,
                     else_branch,
                     counters,
                     new_functions,
@@ -666,6 +677,8 @@ fn simplify_lines(
                         let mut body_copy = body.clone();
                         replace_vars_for_unroll(&mut body_copy, iterator, unroll_index, i, &internal_variables);
                         unrolled_lines.extend(simplify_lines(
+                            functions,
+                            0,
                             &body_copy,
                             counters,
                             new_functions,
@@ -689,6 +702,8 @@ fn simplify_lines(
                 let valid_aux_vars_in_array_manager_before = array_manager.valid.clone();
                 array_manager.valid.clear();
                 let simplified_body = simplify_lines(
+                    functions,
+                    0,
                     body,
                     counters,
                     new_functions,
@@ -763,6 +778,16 @@ fn simplify_lines(
                 return_data,
                 line_number,
             } => {
+                let function = functions
+                    .get(function_name)
+                    .expect("Function used but not defined: {function_name}");
+                if return_data.len() != function.n_returned_vars {
+                    panic!(
+                        "Expected {} returned vars in call to {function_name}",
+                        function.n_returned_vars
+                    );
+                }
+
                 let simplified_args = args
                     .iter()
                     .map(|arg| simplify_expr(arg, &mut res, counters, array_manager, const_malloc))
@@ -776,6 +801,11 @@ fn simplify_lines(
             }
             Line::FunctionRet { return_data } => {
                 assert!(!in_a_loop, "Function return inside a loop is not currently supported");
+                assert!(
+                    return_data.len() == n_returned_vars,
+                    "Wrong number of return values in return statement; expected {n_returned_vars} but got {}",
+                    return_data.len()
+                );
                 let simplified_return_data = return_data
                     .iter()
                     .map(|ret| simplify_expr(ret, &mut res, counters, array_manager, const_malloc))
diff --git a/crates/lean_compiler/tests/test_compiler.rs b/crates/lean_compiler/tests/test_compiler.rs
index 2267bbe9..3142c6d7 100644
--- a/crates/lean_compiler/tests/test_compiler.rs
+++ b/crates/lean_compiler/tests/test_compiler.rs
@@ -38,6 +38,36 @@ fn test_duplicate_constant_name() {
     compile_and_run(program.to_string(), (&[], &[]), DEFAULT_NO_VEC_RUNTIME_MEMORY, false);
 }
 
+#[test]
+#[should_panic]
+fn test_wrong_n_returned_vars_1() {
+    let program = r#"
+    fn main() {
+        a, b = f();
+    }
+
+    fn f() -> 1 {
+        return 0;
+    }
+    "#;
+    compile_and_run(program.to_string(), (&[], &[]), DEFAULT_NO_VEC_RUNTIME_MEMORY, false);
+}
+
+#[test]
+#[should_panic]
+fn test_wrong_n_returned_vars_2() {
+    let program = r#"
+    fn main() {
+        a = f();
+    }
+
+    fn f() -> 1 {
+        return 0, 1;
+    }
+    "#;
+    compile_and_run(program.to_string(), (&[], &[]), DEFAULT_NO_VEC_RUNTIME_MEMORY, false);
+}
+
 #[test]
 fn test_fibonacci_program() {
     // a program to check the value of the 30th Fibonacci number (832040)