diff --git a/lib/builtins/main.hyd b/lib/builtins/main.hyd
index 2050b8a..b406e60 100644
--- a/lib/builtins/main.hyd
+++ b/lib/builtins/main.hyd
@@ -4,5 +4,5 @@ comb reduce_or (
 	a: Logic
 	)
 	-> Logic<1> {
-	
+	reduce_or(a)
 }
diff --git a/src/frontend.rs b/src/frontend.rs
index 29436b3..07d0ce5 100644
--- a/src/frontend.rs
+++ b/src/frontend.rs
@@ -196,6 +196,13 @@ impl Context {
                     .map(|expr| self.type_expression(expr))
                     .collect::<Result<Vec<_>, _>>()?;
                 let called = self.try_get_callable(call.name.fragment())?;
+                let called_callable = self.callables.get(called);
+                if args_resolved.len() != called_callable.argcount() {
+                    return Err(CompileError::new(CompileErrorKind::BadArgCount {
+                        received: args_resolved.len(),
+                        expected: called_callable.argcount(),
+                    }));
+                }
                 typed_ir::Expr {
                     id,
                     kind: typed_ir::ExprKind::Call {
diff --git a/src/frontend/callable.rs b/src/frontend/callable.rs
index 5025419..68be24f 100644
--- a/src/frontend/callable.rs
+++ b/src/frontend/callable.rs
@@ -1,5 +1,4 @@
-use super::types::{Type, TypingContext};
-use std::collections::HashMap;
+use super::types::{GenericArg, Type, TypingContext};
 
 #[derive(Debug, Copy, Clone, PartialOrd, PartialEq, Eq, Ord)]
 pub struct CallableId(pub usize);
@@ -38,6 +37,7 @@ impl CallableContext {
             bitnot: CallableId(1),
             reduce_or: CallableId(2),
         };
+        let logic1 = typectx.make_logic_size(1);
         Self {
             callables: vec![
                 Callable {
@@ -52,8 +52,8 @@ impl CallableContext {
                 },
                 Callable {
                     name: "builtin::reduce_or".to_string(),
-                    args: vec![],
-                    ret_type: Some(typectx.primitives.logic),
+                    args: vec![(Some("a".to_string()), typectx.primitives.logic)],
+                    ret_type: Some(logic1),
                 },
             ],
             builtins,
diff --git a/src/frontend/types.rs b/src/frontend/types.rs
index cef1dc3..367e031 100644
--- a/src/frontend/types.rs
+++ b/src/frontend/types.rs
@@ -125,6 +125,12 @@ impl TypingContext {
         }
     }
 
+    pub fn make_logic_size(&mut self, width: u32) -> Type {
+        let widthnum = self.make_elabnum_u32(width);
+        self.parameterize(self.primitives.logic, &[GenericArg::Elab(widthnum)])
+            .unwrap()
+    }
+
     pub fn parameterize(&mut self, typ: Type, params: &[GenericArg]) -> Option<Type> {
         // TODO: return proper error type here
         match &self.get(typ).kind {