diff --git a/core/src/main/java/org/lflang/generator/c/CGenerator.java b/core/src/main/java/org/lflang/generator/c/CGenerator.java
index 60e25e2ca9..040178b84f 100644
--- a/core/src/main/java/org/lflang/generator/c/CGenerator.java
+++ b/core/src/main/java/org/lflang/generator/c/CGenerator.java
@@ -1453,7 +1453,7 @@ private void generateStartTimeStep(ReactorInstance instance) {
 
           temp.pr("// Add port " + port.getFullName() + " to array of is_present fields.");
 
-          if (port.getParent().equals(instance)) {
+          if (!port.getParent().equals(instance)) {
             // The port belongs to contained reactor, so we also have
             // iterate over the instance bank members.
             temp.startScopedBlock();