diff --git a/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt b/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt
index bbd3663..8c509a7 100644
--- a/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt
+++ b/tsvm_core/src/net/torvald/tsvm/GraphicsJSR223Delegate.kt
@@ -1618,15 +1618,11 @@ class GraphicsJSR223Delegate(private val vm: VM) {
         }
 
         // cover up top two and bottom two lines with current border colour
-        val lines = arrayOf(0, 1, height - 2, height - 1)
-        for (x in 0 until width) {
-            for (y in lines) {
-                val dest = (y * width + x) * 3
-                vm.poke(outputRGBAddr + dest + 0, vm.peek(-1299457)!!)
-                vm.poke(outputRGBAddr + dest + 1, vm.peek(-1299458)!!)
-                vm.poke(outputRGBAddr + dest + 2, vm.peek(-1299459)!!)
-            }
-        }
+        val destT = 0
+        val destB = (height - 2) * width * 3
+        val col = (vm.peek(-1299457)!!.toUint() shl 16) or (vm.peek(-1299458)!!.toUint() shl 8) or vm.peek(-1299459)!!.toUint()
+        vm.memsetI24(outputRGBAddr.toInt() + destT, col, width * 6)
+        vm.memsetI24(outputRGBAddr.toInt() + destB, col, width * 6)
     }
     
     fun tevYcocgToRGB(yBlock: IntArray, coBlock: IntArray, cgBlock: IntArray): IntArray {
diff --git a/tsvm_core/src/net/torvald/tsvm/VM.kt b/tsvm_core/src/net/torvald/tsvm/VM.kt
index 10c6c5b..eeab9fe 100644
--- a/tsvm_core/src/net/torvald/tsvm/VM.kt
+++ b/tsvm_core/src/net/torvald/tsvm/VM.kt
@@ -549,6 +549,19 @@ class VM(
         return dest
     }
 
+    fun memsetI24(dest: Int, ch: Int, countInBytes: Int): Int {
+        val r = ch.ushr(16).and(255).toByte()
+        val g = ch.ushr(8).and(255).toByte()
+        val b = ch.ushr(0).and(255).toByte()
+        val incVec = if (dest >= 0) 1L else -1L
+        for (i in 0 until countInBytes step 3) {
+            poke(dest + (i + 0)*incVec, r)
+            poke(dest + (i + 1)*incVec, g)
+            poke(dest + (i + 2)*incVec, b)
+        }
+        return dest
+    }
+
     fun bulkPeekShort(from: Int, to: ShortArray, sizeInBytes: Int) {
         if (from !in 0..8*1024*1024) throw IllegalArgumentException()
         UnsafeHelper.memcpyRaw(null, usermem.ptr + from, to, UnsafeHelper.getArrayOffset(to), sizeInBytes.toLong())