diff --git a/src/debugger/CartDebug.hxx b/src/debugger/CartDebug.hxx
index d174f9880..8d1b91924 100644
--- a/src/debugger/CartDebug.hxx
+++ b/src/debugger/CartDebug.hxx
@@ -300,7 +300,7 @@ class CartDebug : public DebuggerSystem
     struct ReservedEquates {
       std::array<bool, 16>  TIARead{false};
       std::array<bool, 64>  TIAWrite{false};
-      std::array<bool, 128>  IOReadWrite{false};
+      std::array<bool, 32>  IOReadWrite{false};
       std::array<bool, 128> ZPRAM{false};
       AddrToLabel Label{};
       bool breakFound{false};
diff --git a/src/debugger/DiStella.hxx b/src/debugger/DiStella.hxx
index 3cf2d71ae..268c0c8d4 100644
--- a/src/debugger/DiStella.hxx
+++ b/src/debugger/DiStella.hxx
@@ -126,10 +126,11 @@ class DiStella
         else
           myReserved.TIAWrite[addr & 0x3F] = true;
       }
-      else if (labfound == AddressType::RIOT)
-        myReserved.IOReadWrite[(addr & 0xFF) - 0x80] = true;
+      else if(labfound == AddressType::RIOT) {
+        myReserved.IOReadWrite[addr & 0x1F] = true;
+      }
       else if (labfound == AddressType::ZP_RAM)
-        myReserved.ZPRAM[(addr & 0xFF) - 0x80] = true;
+        myReserved.ZPRAM[addr & 0x7F] = true;
     }
 
   private: