diff --git a/script.js b/script.js
index f944a11..39db513 100644
--- a/script.js
+++ b/script.js
@@ -64,7 +64,9 @@ addEventListener('DOMContentLoaded', () => {
     const mask = options.mask.value
     const size = Number(options.size.value)
     const scale = Number(options.scale.value)
-    const gap = Math.min(Number(options.gap.value), scale) // not more than 1 module scaled size
+    // not more than (half of 1 scaled module size) - 1
+    // at gap=scale/2 squares disappear
+    const gap = Math.min(Number(options.gap.value), intDiv(scale, 2) - 1)
 
     const wh = scale - gap * 2 // width&height for 1 module with grid gap