diff --git a/mvn-assembler/Cargo.toml b/mvn-assembler/Cargo.toml
index 1517dfc..7a42f5f 100644
--- a/mvn-assembler/Cargo.toml
+++ b/mvn-assembler/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "mvn-assembler"
-version = "0.1.1"
+version = "0.1.2"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
diff --git a/mvn-assembler/src/processor/validator.rs b/mvn-assembler/src/processor/validator.rs
index b33cdb6..adbf86a 100644
--- a/mvn-assembler/src/processor/validator.rs
+++ b/mvn-assembler/src/processor/validator.rs
@@ -1,6 +1,8 @@
+use std::collections::BTreeSet;
+
 use crate::types::{mneumonic, Instruction, Line, Operand};
 
-use crate::processor::address::{Address, AddressedProgram, LabelMap};
+use crate::processor::address::{Address, AddressedLine, AddressedProgram, LabelMap};
 
 use super::MvnReportError;
 
@@ -10,6 +12,8 @@ pub fn validate<'a, 'b>(
     program: &'a AddressedProgram<'b>,
     label_map: &'a LabelMap<'b>,
 ) -> ValidatorResult<'b> {
+    let validator = ProgramValidator::new(program, label_map);
+    validator.validate()?;
     for line in program.lines.iter() {
         let validator = LineValidator::new(&line.line, &line.address, label_map);
         validator.validate()?;
@@ -17,12 +21,52 @@ pub fn validate<'a, 'b>(
     Ok(())
 }
 
+// `label_map` is not required right now but it might be in future tests,
+// so keep it in the struct despite being dead code
+#[allow(dead_code)]
+struct ProgramValidator<'a, 'b> {
+    program: &'a AddressedProgram<'b>,
+    label_map: &'a LabelMap<'b>,
+}
+
 struct LineValidator<'a, 'b> {
     line: &'a Line<'b>,
     address: &'a Address,
     label_map: &'a LabelMap<'b>,
 }
 
+/* Every validator function's name should
+ * answer the question: "Does the program
+ * contain {name}?"
+ */
+
+impl<'b> ProgramValidator<'_, 'b> {
+    pub fn validate(self) -> ValidatorResult<'b> {
+        self.labels_defined_more_than_once()?;
+        Ok(())
+    }
+
+    fn labels_defined_more_than_once(&self) -> ValidatorResult<'b> {
+        let mut label_set = BTreeSet::new();
+        for AddressedLine { address: _, line } in self
+            .program
+            .lines
+            .iter()
+            .filter(|addressed_line| addressed_line.line.label.is_some())
+        {
+            if let Some(label) = &line.label {
+                if !label_set.insert(label.value.clone()) {
+                    return Err(MvnReportError::new(
+                        label.position,
+                        Some("label was already defined".to_string()),
+                    ));
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
 impl<'b> LineValidator<'_, 'b> {
     pub fn validate(self) -> ValidatorResult<'b> {
         self.numeric_operand_on_import_export()?;
@@ -33,11 +77,6 @@ impl<'b> LineValidator<'_, 'b> {
         Ok(())
     }
 
-    /* Every validator function's name should
-     * answer the question: "Does the program
-     * contain {name}?"
-     */
-
     fn numeric_operand_on_import_export(&self) -> ValidatorResult<'b> {
         match &self.line.operation.instruction.value {
             Instruction::Relational(_) => match &self.line.operation.operand.value {
@@ -133,6 +172,12 @@ impl<'b> LineValidator<'_, 'b> {
     }
 }
 
+impl<'a, 'b> ProgramValidator<'a, 'b> {
+    fn new(program: &'a AddressedProgram<'b>, label_map: &'a LabelMap<'b>) -> Self {
+        Self { program, label_map }
+    }
+}
+
 impl<'a, 'b> LineValidator<'a, 'b> {
     fn new(line: &'a Line<'b>, address: &'a Address, label_map: &'a LabelMap<'b>) -> Self {
         Self {
@@ -169,6 +214,7 @@ mod tests {
      */
 
     struct TestProgram {
+        repeated_label: bool,
         import: Operand<'static>,
         constant: u32,
         position: Operand<'static>,
@@ -179,6 +225,7 @@ mod tests {
     impl Default for TestProgram {
         fn default() -> Self {
             Self {
+                repeated_label: false,
                 import: "IMPORT".into(),
                 constant: 0x1,
                 position: 0x100.into(),
@@ -195,6 +242,11 @@ mod tests {
         }
 
         fn render(self) -> (AddressedProgram<'static>, LabelMap<'static>) {
+            let main_label: Label = if self.repeated_label {
+                "ONE".into()
+            } else {
+                "MAIN".into()
+            };
             let main_position = if let Operand::Numeric(immediate) = self.position {
                 immediate
             } else {
@@ -256,7 +308,7 @@ mod tests {
                         ..Default::default()
                     },
                     Line::new(
-                        Some(Token::new(Position::new(8, 1), "MAIN".into())),
+                        Some(Token::new(Position::new(8, 1), main_label)),
                         Operation::new(
                             Token::new(
                                 Position::new(8, 9),
@@ -318,10 +370,20 @@ mod tests {
         assert!(test_program.validate().is_ok());
     }
 
+    #[test]
+    fn repeated_labels_should_fail() {
+        let test_program = TestProgram {
+            repeated_label: true,
+            ..Default::default()
+        };
+        assert!(test_program.validate().is_err());
+    }
+
     // #[test]
     // fn symbolic_operand_on_import_export_should_pass() {
 
     // }
+
     #[test]
     fn numeric_operand_on_import_export_should_fail() {
         let test_program = TestProgram {
diff --git a/mvn-utils/src/types.rs b/mvn-utils/src/types.rs
index 4b208e6..adb35de 100644
--- a/mvn-utils/src/types.rs
+++ b/mvn-utils/src/types.rs
@@ -64,3 +64,12 @@ impl<T: fmt::UpperHex> fmt::UpperHex for Token<T> {
         write!(f, "{:X}", &self.value)
     }
 }
+
+impl<T: Clone> Clone for Token<T> {
+    fn clone(&self) -> Self {
+        Self {
+            value: self.value.clone(),
+            position: self.position,
+        }
+    }
+}