diff --git a/src/devices/cpu/mcs51/mcs51.h b/src/devices/cpu/mcs51/mcs51.h
index 32c956ef342f8..40397cf81ad66 100644
--- a/src/devices/cpu/mcs51/mcs51.h
+++ b/src/devices/cpu/mcs51/mcs51.h
@@ -81,7 +81,7 @@ class mcs51_cpu_device : public cpu_device
 	virtual uint64_t execute_clocks_to_cycles(uint64_t clocks) const noexcept override { return (clocks + 12 - 1) / 12; }
 	virtual uint64_t execute_cycles_to_clocks(uint64_t cycles) const noexcept override { return (cycles * 12); }
 	virtual uint32_t execute_min_cycles() const noexcept override { return 1; }
-	virtual uint32_t execute_max_cycles() const noexcept override { return 2+2; }
+	virtual uint32_t execute_max_cycles() const noexcept override { return 4+2; } // max opcode cycles + irq
 	virtual void execute_run() override;
 	virtual void execute_set_input(int inputnum, int state) override;