1 files changed, 1 insertions, 0 deletions

diff --git a/ppmsum.cpp b/ppmsum.cpp
index 927efa8..506b964 100644
--- a/ppmsum.cpp
+++ b/ppmsum.cpp
@@ -36,6 +36,7 @@ void PPMSum::irq() {
 			index = 0;
 		} else {
 			index++;
+			index &= 0xf;
 		}
 		
 	} else if(sr & 0x04) {