1 files changed, 2 insertions, 1 deletions

diff --git a/isa/isa.h b/isa/isa.h
index 1ad5a77..84a783c 100644
--- a/isa/isa.h
+++ b/isa/isa.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <cstdint>
 #include <functional>
 #include <optional>
 
@@ -49,7 +50,7 @@ struct instruction_context {
     unsigned int next_pc;                       // includes IF
     std::optional<unsigned int> init_address;   // includes DF
     std::optional<unsigned int> final_address;  // includes DF
-    std::optional<unsigned int> ctlval;
+    std::optional<std::uint_fast32_t> ctlval;   // control registers may be larger than 16 bits (e.g. TT_BITS)
     std::optional<unsigned int> data;
     std::optional<unsigned int> acc;
     std::optional<bool> link;