diff --git a/src/main.rs b/src/main.rs
index 236523a..d214f35 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -75,7 +75,7 @@ fn main() {
   let system = match args.system {
     SystemArg::Basic => BasicSystemBuilder::build(romfile.unwrap(), (), platform.provider()),
     SystemArg::Easy => Easy6502SystemBuilder::build(romfile.unwrap(), (), platform.provider()),
-    SystemArg::Klaus => KlausSystemBuilder::build(romfile.unwrap(), (), platform.provider()),
+    SystemArg::Klaus => KlausSystemBuilder::build(romfile.unwrap(), None, platform.provider()),
     SystemArg::Pet => PetSystemBuilder::build(
       PetSystemRoms::from_disk(),
       PetSystemConfig { mapping },
diff --git a/src/systems/klaus.rs b/src/systems/klaus.rs
index 3f90f47..7388b93 100644
--- a/src/systems/klaus.rs
+++ b/src/systems/klaus.rs
@@ -1,10 +1,12 @@
-use instant::{Duration, Instant};
+use instant::Duration;
 
 use crate::cpu::Mos6502;
 use crate::memory::BlockMemory;
 use crate::platform::{PlatformProvider, WindowConfig};
 use crate::roms::RomFile;
 use crate::systems::System;
+use std::cell::Cell;
+use std::rc::Rc;
 use std::sync::Arc;
 
 use super::SystemBuilder;
@@ -12,33 +14,34 @@ use super::SystemBuilder;
 /// A factory for creating a system that runs Klaus Dormann's 6502 CPU test suite.
 pub struct KlausSystemBuilder;
 
-impl SystemBuilder<KlausSystem, RomFile, ()> for KlausSystemBuilder {
-  fn build(rom: RomFile, _config: (), _platform: Arc<dyn PlatformProvider>) -> Box<dyn System> {
+impl SystemBuilder<KlausSystem, RomFile, Option<Rc<Cell<u16>>>> for KlausSystemBuilder {
+  fn build(
+    rom: RomFile,
+    config: Option<Rc<Cell<u16>>>,
+    _platform: Arc<dyn PlatformProvider>,
+  ) -> Box<dyn System> {
     let rom = BlockMemory::from_file(0x10000, rom);
     let mut cpu = Mos6502::new(Box::new(rom));
 
     cpu.registers.pc.load(0x0400);
 
-    Box::new(KlausSystem {
-      cpu,
-      last_report: Instant::now(),
-    })
+    Box::new(KlausSystem { cpu, pc: config })
   }
 }
 
 /// A system used to run Klaus Dormann's 6502 CPU test suite.
 pub struct KlausSystem {
   cpu: Mos6502,
-  last_report: Instant,
+  pc: Option<Rc<Cell<u16>>>,
 }
 
 impl System for KlausSystem {
   fn tick(&mut self) -> Duration {
-    if self.last_report.elapsed().as_secs() > 1 {
-      println!("PC: {:04x}", self.cpu.registers.pc.address());
-      self.last_report = Instant::now();
-    };
-    Duration::from_secs_f64(1.0 / 1_000_000.0) * self.cpu.tick().into()
+    self.cpu.tick();
+    if let Some(pc) = &self.pc {
+      pc.set(self.cpu.registers.pc.address());
+    }
+    Duration::ZERO
   }
 
   fn reset(&mut self) {
@@ -47,3 +50,27 @@ impl System for KlausSystem {
 
   fn render(&mut self, _framebuffer: &mut [u8], _window: WindowConfig) {}
 }
+
+#[cfg(test)]
+mod tests {
+  use crate::{
+    platform::{Platform, TextPlatform},
+    roms::DiskLoadable,
+  };
+
+  use super::*;
+
+  #[test]
+  fn test_klaus() {
+    let roms = RomFile::from_file("bin/klaus.bin");
+    let platform = TextPlatform::new();
+    let pc = Rc::new(Cell::new(0));
+    let mut system = KlausSystemBuilder::build(roms, Some(pc.clone()), platform.provider());
+
+    for _ in 0..=100000000 {
+      system.tick();
+    }
+
+    assert_eq!(pc.get(), 0x3469);
+  }
+}