diff --git a/tridoraemu/framebuffer.go b/tridoraemu/framebuffer.go
index a3a92ab..4586287 100644
--- a/tridoraemu/framebuffer.go
+++ b/tridoraemu/framebuffer.go
@@ -75,16 +75,17 @@ func (f *Framebuffer) write(value word, byteaddr word) (error) {
 }
 
 func (f *Framebuffer) readVmem() word {
-	result := f.vmem[f.readAddr]
+	result := f.vmem[f.readAddr & (VmemWords - 1)]
 	f.readAddr += 1
 	return result
 }
 
 func (f *Framebuffer) writeVmem(value word) {
-	f.vmem[f.writeAddr] = value
+	vaddr := f.writeAddr & (VmemWords - 1)
+	f.vmem[vaddr] = value
 
-	y := f.writeAddr / WordsPerLine
-	x := f.writeAddr % WordsPerLine * PixelPerWord
+	y := vaddr / WordsPerLine
+	x := vaddr % WordsPerLine * PixelPerWord
 
 	for i := 0; i < PixelPerWord; i++ {
 		pixel := (value & PixelMask) >> (VmemWidth - BitsPerPixel)