diff --git a/src/main/java/org/broad/igv/sam/AlignmentRenderer.java b/src/main/java/org/broad/igv/sam/AlignmentRenderer.java
index 5c9cb8046..a67b6362e 100644
--- a/src/main/java/org/broad/igv/sam/AlignmentRenderer.java
+++ b/src/main/java/org/broad/igv/sam/AlignmentRenderer.java
@@ -705,7 +705,9 @@ private void drawAlignment(
 
             // Check if block is in visible rectangle
             if (blockPxEnd < 0) {
-                blockChromStart = blocks[blockIx + 1].getStart(); // start position for the next block
+                if(blockIx + 1 < blocks.length) {
+                    blockChromStart = blocks[blockIx + 1].getStart(); // start position for the next block
+                }
                 continue;
             } else if (blockPxStart > rowRect.x + rowRect.width) {
                 break;