diff --git a/core/src/main/java/org/lflang/diagram/synthesis/postprocessor/ReactorPortAdjustment.java b/core/src/main/java/org/lflang/diagram/synthesis/postprocessor/ReactorPortAdjustment.java
new file mode 100644
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+++ b/core/src/main/java/org/lflang/diagram/synthesis/postprocessor/ReactorPortAdjustment.java
@@ -0,0 +1,175 @@
+/*************
+ * Copyright (c) 2023, Kiel University.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ ***************/
+package org.lflang.diagram.synthesis.postprocessor;
+
+import com.google.inject.Binder;
+import com.google.inject.Guice;
+import com.google.inject.Scopes;
+import com.google.inject.TypeLiteral;
+import de.cau.cs.kieler.klighd.IStyleModifier;
+import de.cau.cs.kieler.klighd.IViewer;
+import de.cau.cs.kieler.klighd.internal.ILayoutRecorder;
+import de.cau.cs.kieler.klighd.kgraph.KGraphElement;
+import de.cau.cs.kieler.klighd.kgraph.KGraphFactory;
+import de.cau.cs.kieler.klighd.kgraph.KNode;
+import de.cau.cs.kieler.klighd.krendering.KRendering;
+import de.cau.cs.kieler.klighd.krendering.KRenderingFactory;
+import de.cau.cs.kieler.klighd.krendering.ViewSynthesisShared;
+import de.cau.cs.kieler.klighd.syntheses.AbstractDiagramSynthesis;
+import java.util.List;
+import javax.inject.Inject;
+import org.eclipse.elk.core.options.CoreOptions;
+import org.eclipse.elk.graph.properties.Property;
+import org.eclipse.xtext.xbase.lib.Extension;
+import org.lflang.diagram.synthesis.LinguaFrancaSynthesis;
+import org.lflang.diagram.synthesis.styles.LinguaFrancaShapeExtensions;
+
+/**
+ * Adjusts the port figures of reactors when fixed side are off to keep the input output indication
+ * correct.
+ *
+ * @author Alexander Schulz-Rosengarten
+ */
+public class ReactorPortAdjustment implements IStyleModifier {
+
+  public static final String ID =
+      "org.lflang.diagram.synthesis.postprocessor.ReactorPortAdjustment";
+
+  /** INTERNAL property to mark node as flipped. */
+  public static final Property<Boolean> FLIPPED =
+      new Property<>("org.lflang.diagram.synthesis.postprocessor.reactor.ports.flipped", false);
+
+  @Inject @Extension private LinguaFrancaShapeExtensions _linguaFrancaShapeExtensions;
+  @Extension private KGraphFactory _kGraphFactory = KGraphFactory.eINSTANCE;
+  private static KRenderingFactory _kRenderingFactory = KRenderingFactory.eINSTANCE;
+
+  /** Register this modifier on a reaction rendering. */
+  public static void apply(KNode node, List<KRendering> renderings) {
+    var rendering = renderings.get(0); // Get first in bank
+    // Add modifier that fixes port positions such that edges are properly attached to the shape
+    var invisible = _kRenderingFactory.createKRotation();
+    // make it ineffective (just for purpose of holding modifier)
+    invisible.setRotation(0);
+    // Add modifier to receive callback after layout
+    invisible.setModifierId(ID);
+    rendering.getStyles().add(invisible);
+  }
+
+  public ReactorPortAdjustment() {
+    // Inject extension
+    if (_linguaFrancaShapeExtensions == null) {
+      var injector =
+          Guice.createInjector(
+              new com.google.inject.Module() {
+                // This Module is created to satisfy ViewSynthesisShared scope of used
+                // synthesis-extensions
+                public void configure(Binder binder) {
+                  binder.bindScope(ViewSynthesisShared.class, Scopes.SINGLETON);
+                  binder
+                      .bind(new TypeLiteral<AbstractDiagramSynthesis<?>>() {})
+                      .toInstance(new LinguaFrancaSynthesis());
+                }
+              });
+      _linguaFrancaShapeExtensions = injector.getInstance(LinguaFrancaShapeExtensions.class);
+    }
+  }
+
+  @Override
+  public boolean modify(IStyleModifier.StyleModificationContext context) {
+    try {
+      KGraphElement node = context.getGraphElement();
+      if (node instanceof KNode) {
+        KNode knode = (KNode) node;
+
+        // Find root node
+        KNode parent = knode;
+        while (parent.eContainer() != null) {
+          parent = (KNode) parent.eContainer();
+        }
+
+        // Get viewer (this is a bit brittle because it fetches the viewer from some internal
+        // property)
+        Object viewer =
+            parent.getAllProperties().entrySet().stream()
+                .filter(
+                    entry ->
+                        entry.getKey().getId().equals("de.cau.cs.kieler.klighd.viewer")
+                            || entry.getKey().getId().equals("klighd.layout.viewer"))
+                .findAny()
+                .map(entry -> entry.getValue())
+                .orElse(null);
+
+        ILayoutRecorder recorder = null;
+        if (viewer instanceof IViewer) {
+          recorder = ((IViewer) viewer).getViewContext().getLayoutRecorder();
+        }
+
+        if (recorder != null) {
+          recorder.startRecording();
+        }
+        for (var port : knode.getPorts()) {
+          var isInput = port.getProperty(LinguaFrancaSynthesis.REACTOR_INPUT).booleanValue();
+          if (!isInput && !port.getProperty(LinguaFrancaSynthesis.REACTOR_OUTPUT)) {
+            continue; // skip
+          }
+
+          var xPos = port.getXpos();
+          var isLeft = xPos < 0;
+          var flip = isInput != isLeft;
+          var isFlipped = port.getProperty(FLIPPED).booleanValue();
+          var needsUpdate = flip != isFlipped;
+
+          if (needsUpdate) {
+            // Remove figure
+            port.getData().removeIf(it -> it instanceof KRendering);
+
+            // Get port type
+            var isMultiport = port.getProperty(LinguaFrancaSynthesis.REACTOR_MULTIPORT);
+            var isBank = port.getProperty(LinguaFrancaSynthesis.REACTOR_HAS_BANK_PORT_OFFSET);
+
+            // Add new figure
+            _linguaFrancaShapeExtensions.addTrianglePort(port, isMultiport, flip);
+            port.setProperty(FLIPPED, flip);
+
+            // Compute new offset
+            var oldOffset = port.getProperty(CoreOptions.PORT_BORDER_OFFSET);
+            var newOffset =
+                LinguaFrancaSynthesis.getReactorPortOffset(!isLeft, isMultiport, isBank);
+
+            // Apply offset directly
+            port.setPos((float) (port.getXpos() + (oldOffset - newOffset)), port.getYpos());
+          }
+        }
+        if (recorder != null) {
+          recorder.stopRecording(0);
+        }
+      }
+    } catch (Exception e) {
+      e.printStackTrace();
+      // do not disturb rendering process
+    }
+    return false;
+  }
+}
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