diff --git a/src/interpreter/environment.rs b/src/interpreter/environment.rs
index 602ee1e..eeaf8c7 100644
--- a/src/interpreter/environment.rs
+++ b/src/interpreter/environment.rs
@@ -49,7 +49,7 @@ impl Environment {
         if self.values.contains_key(&name.lexeme as &str) {
             Err(InterpreterError::new(
                 name,
-                &format!("variables '{}' already defined in scope", name.lexeme),
+                &format!("variable '{}' already defined in scope", name.lexeme),
             ))
         } else {
             self.values.insert(name.lexeme.clone(), value);