diff --git a/crates/lean_compiler/src/lib.rs b/crates/lean_compiler/src/lib.rs
index 3f5c4f94..135c5815 100644
--- a/crates/lean_compiler/src/lib.rs
+++ b/crates/lean_compiler/src/lib.rs
@@ -24,7 +24,7 @@ pub fn compile_program(program: &str) -> (Bytecode, BTreeMap<usize, String>) {
     let intermediate_bytecode = compile_to_intermediate_bytecode(simple_program).unwrap();
     // println!("Intermediate Bytecode:\n\n{}", intermediate_bytecode.to_string());
     let compiled = compile_to_low_level_bytecode(intermediate_bytecode).unwrap();
-    // println!("Compiled Program:\n\n{}", compiled.to_string());
+    println!("Compiled Program:\n\n{}", compiled.to_string());
     (compiled, function_locations)
 }
 
diff --git a/crates/lean_compiler/src/parser.rs b/crates/lean_compiler/src/parser.rs
index 2fd54bfc..80b90384 100644
--- a/crates/lean_compiler/src/parser.rs
+++ b/crates/lean_compiler/src/parser.rs
@@ -51,13 +51,18 @@ pub fn parse_program(input: &str) -> Result<(Program, BTreeMap<usize, String>),
         match pair.as_rule() {
             Rule::constant_declaration => {
                 let (name, value) = parse_constant_declaration(pair, &constants)?;
-                constants.insert(name, value);
+                if constants.insert(name.clone(), value).is_some() {
+                    panic!("Multiply defined constant: {name}");
+                }
             }
             Rule::function => {
                 let location = pair.line_col().0;
                 let function = parse_function(pair, &constants, &mut trash_var_count)?;
-                function_locations.insert(location, function.name.clone());
-                functions.insert(function.name.clone(), function);
+                let name = function.name.clone();
+                function_locations.insert(location, name.clone());
+                if functions.insert(name.clone(), function).is_some() {
+                    panic!("Multiply defined function: {name}");
+                }
             }
             Rule::EOI => break,
             _ => {}
diff --git a/crates/lean_compiler/tests/test_compiler.rs b/crates/lean_compiler/tests/test_compiler.rs
index a78cfcd2..6743c095 100644
--- a/crates/lean_compiler/tests/test_compiler.rs
+++ b/crates/lean_compiler/tests/test_compiler.rs
@@ -3,6 +3,40 @@ use lean_vm::*;
 use p3_symmetric::Permutation;
 use utils::{get_poseidon16, get_poseidon24};
 
+#[test]
+#[should_panic]
+fn test_duplicate_function_name() {
+    let program = r#"
+    fn a() -> 1 {
+        return 0;
+    }
+
+    fn a() -> 1 {
+        return 1;
+    }
+
+    fn main() {
+        a();
+        return;
+    }
+    "#;
+    compile_and_run(program, &[], &[], false);
+}
+
+#[test]
+#[should_panic]
+fn test_duplicate_constant_name() {
+    let program = r#"
+    const A = 1;
+    const A = 0;
+
+    fn main() {
+        return;
+    }
+    "#;
+    compile_and_run(program, &[], &[], false);
+}
+
 #[test]
 fn test_fibonacci_program() {
     // a program to check the value of the 30th Fibonacci number (832040)