diff --git a/mute-interpreter/src/evaluator.rs b/mute-interpreter/src/evaluator.rs
index 92e52a0..873607d 100644
--- a/mute-interpreter/src/evaluator.rs
+++ b/mute-interpreter/src/evaluator.rs
@@ -181,7 +181,8 @@ mod test {
     #[case("(error \"this failed\")", "error: this failed")]
     #[case("(error? (error \"this failed\"))", "true")]
     #[case("(error? 69)", "false")]
-    #[case("(str 1 2 3)", "error: expected 1 args, got 3")]
+    #[case("(str 1 2 3)", "error: expected 1 arg(s), got 3")]
+    #[case("(hashmap 1 2 3)", "error: expected 4 arg(s), got 3")]
     // Meta
     #[case("(eval (list + 1 1))", "2")]
     #[case("(apply + (list 1 2 3))", "6")]
diff --git a/mute-interpreter/src/macros.rs b/mute-interpreter/src/macros.rs
index 814915a..219d320 100644
--- a/mute-interpreter/src/macros.rs
+++ b/mute-interpreter/src/macros.rs
@@ -1,15 +1,16 @@
+// TODO: argument count checking should happen at parse time, not at runtime
 #[macro_export]
 macro_rules! arg_count {
     ($expected:expr, $given:expr) => {
         if $expected != $given {
-            return Node::Error(format!("expected {} args, got {}", $expected, $given));
+            return Node::Error(format!("expected {} arg(s), got {}", $expected, $given));
         }
     };
 
     (modulo: $modulo:expr, $given:expr) => {
         if $given % $modulo != 0 {
             return Node::Error(format!(
-                "expected {} args, got {}",
+                "expected {} arg(s), got {}",
                 ($given / $modulo) * $modulo + $modulo,
                 $given,
             ));