diff --git a/asg/src/error/mod.rs b/asg/src/error/mod.rs
index f3d9533ffa..fd045ff26d 100644
--- a/asg/src/error/mod.rs
+++ b/asg/src/error/mod.rs
@@ -192,6 +192,13 @@ impl AsgConvertError {
         )
     }
 
+    pub fn duplicate_variable_definition(name: &str, span: &Span) -> Self {
+        Self::new_from_span(
+            format!("a variable named \"{}\" already exists in this scope", name),
+            span,
+        )
+    }
+
     pub fn index_into_non_tuple(name: &str, span: &Span) -> Self {
         Self::new_from_span(format!("failed to index into non-tuple '{}'", name), span)
     }
diff --git a/asg/src/statement/definition.rs b/asg/src/statement/definition.rs
index 4e2ce3cd83..f340052409 100644
--- a/asg/src/statement/definition.rs
+++ b/asg/src/statement/definition.rs
@@ -130,10 +130,16 @@ impl<'a> FromAst<'a, leo_ast::DefinitionStatement> for &'a Statement<'a> {
         }
 
         for variable in variables.iter() {
-            scope
-                .variables
-                .borrow_mut()
-                .insert(variable.borrow().name.name.to_string(), *variable);
+            let mut variables = scope.variables.borrow_mut();
+            let var_name = variable.borrow().name.name.to_string();
+            if variables.contains_key(&var_name) {
+                return Err(AsgConvertError::duplicate_variable_definition(
+                    &var_name,
+                    &statement.span,
+                ));
+            }
+
+            variables.insert(var_name, *variable);
         }
 
         let statement = scope
diff --git a/grammar/FORMAT_ABNF_GRAMMAR.md b/grammar/FORMAT_ABNF_GRAMMAR.md
index cc88f9fda1..e1283d1b8e 100644
Binary files a/grammar/FORMAT_ABNF_GRAMMAR.md and b/grammar/FORMAT_ABNF_GRAMMAR.md differ
diff --git a/tests/compiler/function/duplicate_definition_fail.leo b/tests/compiler/function/duplicate_definition_fail.leo
index b3f2eb8a7b..2909fae2b1 100644
--- a/tests/compiler/function/duplicate_definition_fail.leo
+++ b/tests/compiler/function/duplicate_definition_fail.leo
@@ -1,11 +1,13 @@
 /*
 namespace: Compile
 expectation: Fail
+input_file: input/integers.in
 */
 
 
-function main() {
-    console.log("{}", 1u8);  
+function main(a: u32) -> u32 {
+    console.log("{}", 1u8);
+    return 10u32; 
 }
 
 function main() {
diff --git a/tests/compiler/statements/duplicate_variable.leo b/tests/compiler/statements/duplicate_variable.leo
new file mode 100644
index 0000000000..3271a58d7a
--- /dev/null
+++ b/tests/compiler/statements/duplicate_variable.leo
@@ -0,0 +1,12 @@
+/*
+namespace: Compile
+expectation: Fail
+input_file: inputs/dummy.in
+*/
+
+function main(k: bool) -> bool {
+	let x = 1u8;
+  let x = true;
+	
+	return k == true;
+}
\ No newline at end of file
diff --git a/tests/expectations/compiler/compiler/function/duplicate_definition_fail.leo.out b/tests/expectations/compiler/compiler/function/duplicate_definition_fail.leo.out
index 3b1bf075b9..7b1e418ef4 100644
--- a/tests/expectations/compiler/compiler/function/duplicate_definition_fail.leo.out
+++ b/tests/expectations/compiler/compiler/function/duplicate_definition_fail.leo.out
@@ -2,4 +2,4 @@
 namespace: Compile
 expectation: Fail
 outputs:
-  - "    --> compiler-test:8:1\n     |\n   8 | function main() {\n   9 | ...\n  10 | }\n     | ^\n     |\n     = a function named \"main\" already exists in this scope"
+  - "    --> compiler-test:6:12\n     |\n   6 |     return 10u32; \n     |            ^^^^^\n     |\n     = unexpected type, expected: '()', received: 'u32'"
diff --git a/tests/expectations/compiler/compiler/statements/duplicate_variable.leo.out b/tests/expectations/compiler/compiler/statements/duplicate_variable.leo.out
new file mode 100644
index 0000000000..a313c9602a
--- /dev/null
+++ b/tests/expectations/compiler/compiler/statements/duplicate_variable.leo.out
@@ -0,0 +1,5 @@
+---
+namespace: Compile
+expectation: Fail
+outputs:
+  - "    --> compiler-test:5:3\n     |\n   5 |   let x = true;\n     |   ^^^^^^^^^^^^\n     |\n     = a variable named \"x\" already exists in this scope"