diff --git a/src/typechecker.rs b/src/typechecker.rs
index d21f70a..9c76e8c 100644
--- a/src/typechecker.rs
+++ b/src/typechecker.rs
@@ -832,6 +832,18 @@ impl TypeChecker {
                             }
                         }
                     }
+                    UnOp::PreInc => {
+                        if !matches!(typed_inner.ty, Type::Int | Type::Float) {
+                            return Err(TypeError {
+                                kind: TypeErrorKind::TypeMismatch(
+                                    Type::Int,
+                                    typed_inner.ty.clone(),
+                                ),
+                                span: inner.span.clone(),
+                            });
+                        }
+                        typed_inner.ty.clone()
+                    }
                 };
                 (
                     TypedExprKind::UnOp(op.clone(), Box::new(typed_inner)),