diff --git a/src/main/java/appeng/blockentity/misc/CondenserBlockEntity.java b/src/main/java/appeng/blockentity/misc/CondenserBlockEntity.java
index 5e3427ad57b..0689ebae53e 100644
--- a/src/main/java/appeng/blockentity/misc/CondenserBlockEntity.java
+++ b/src/main/java/appeng/blockentity/misc/CondenserBlockEntity.java
@@ -110,28 +110,25 @@ public void addPower(double rawPower) {
 
     private void fillOutput() {
         var requiredPower = this.getRequiredPower();
-        var output = this.getOutput();
-        while (requiredPower <= this.getStoredPower() && !output.isEmpty() && requiredPower > 0) {
-            if (this.canAddOutput(output)) {
+        while (requiredPower <= this.getStoredPower() && !getOutput().isEmpty() && requiredPower > 0) {
+            if (this.canAddOutput()) {
                 this.setStoredPower(this.getStoredPower() - requiredPower);
-                this.addOutput(output);
+                this.addOutput();
             } else {
                 break;
             }
         }
     }
 
-    private boolean canAddOutput(ItemStack output) {
-        return this.outputSlot.insertItem(0, output, true).isEmpty();
+    boolean canAddOutput() {
+        return this.outputSlot.insertItem(0, getOutput(), true).isEmpty();
     }
 
     /**
      * make sure you validate with canAddOutput prior to this.
-     *
-     * @param output to be added output
      */
-    private void addOutput(ItemStack output) {
-        this.outputSlot.insertItem(0, output, false);
+    private void addOutput() {
+        this.outputSlot.insertItem(0, getOutput(), false);
     }
 
     InternalInventory getOutputSlot() {
@@ -200,6 +197,11 @@ public ItemStack getStackInSlot(int slot) {
             return ItemStack.EMPTY;
         }
 
+        @Override
+        public boolean isItemValid(int slot, ItemStack stack) {
+            return canAddOutput();
+        }
+
         @Override
         public void setItemDirect(int slotIndex, ItemStack stack) {
             if (!stack.isEmpty()) {
@@ -209,6 +211,9 @@ public void setItemDirect(int slotIndex, ItemStack stack) {
 
         @Override
         public ItemStack insertItem(int slot, ItemStack stack, boolean simulate) {
+            if (!canAddOutput()) {
+                return stack;
+            }
             if (!simulate && !stack.isEmpty()) {
                 CondenserBlockEntity.this.addPower(stack.getCount());
             }
diff --git a/src/main/java/appeng/blockentity/misc/CondenserMEStorage.java b/src/main/java/appeng/blockentity/misc/CondenserMEStorage.java
index 77c9ea28621..c1bce57a656 100644
--- a/src/main/java/appeng/blockentity/misc/CondenserMEStorage.java
+++ b/src/main/java/appeng/blockentity/misc/CondenserMEStorage.java
@@ -37,6 +37,9 @@ class CondenserMEStorage implements MEStorage {
     @Override
     public long insert(AEKey what, long amount, Actionable mode, IActionSource source) {
         MEStorage.checkPreconditions(what, amount, mode, source);
+        if (!target.canAddOutput()) {
+            return 0;
+        }
         if (mode == Actionable.MODULATE) {
             this.target.addPower(amount / what.getAmountPerOperation());
         }