diff --git a/source/build/src/engine.cpp b/source/build/src/engine.cpp
index 764352042..759d1b47e 100644
--- a/source/build/src/engine.cpp
+++ b/source/build/src/engine.cpp
@@ -11057,7 +11057,7 @@ void updatesectorz(int32_t const x, int32_t const y, int32_t const z, int16_t *
 
     if ((unsigned)*sectnum >= (unsigned)numsectors)
     {
-        if ((unsigned)*sectnum < (unsigned)numsectors + MAXSECTORS)
+        if (*sectnum >= MAXSECTORS && (unsigned)*sectnum < (unsigned)numsectors + MAXSECTORS)
         {
             *sectnum -= MAXSECTORS;
             nofirstzcheck = true;