diff --git a/src/main/jastadd/JastAddAPIExtension.jadd b/src/main/jastadd/JastAddAPIExtension.jadd
index 8c4e3b831a11e67b3fe689b42799349cb54bbb56..476bd816cf52d389811adf4d979081368572aeaf 100644
--- a/src/main/jastadd/JastAddAPIExtension.jadd
+++ b/src/main/jastadd/JastAddAPIExtension.jadd
@@ -26,7 +26,7 @@ aspect JastAddAPIExtension {
       if (child instanceof JastAddList) {
         result += child.numChildren();
       } else if (child instanceof Opt) {
-        if (getChild(0).numChildren() != 0) {
+        if (child.numChildren() != 0) {
           result += 1;
         }
       } else {