diff --git a/src/io.c b/src/io.c
index e6ab88453..3df413f9b 100644
--- a/src/io.c
+++ b/src/io.c
@@ -329,7 +329,7 @@ io_debug_check_addr(uint16_t addr)
         }
     }
     if (set_trap)
-        trap = 4;
+        trap |= 4;
 }
 
 uint8_t
diff --git a/src/mem/mem.c b/src/mem/mem.c
index 887720d3d..567c17634 100644
--- a/src/mem/mem.c
+++ b/src/mem/mem.c
@@ -209,7 +209,7 @@ mem_debug_check_addr(uint32_t addr, int write)
         }
     }
     if (set_trap)
-        trap = 4;
+        trap |= 4;
 }
 
 int