diff --git a/src/lib/components/list-editor/list-editor.svelte b/src/lib/components/list-editor/list-editor.svelte
index e8ce0ff06..4cf0652dc 100644
--- a/src/lib/components/list-editor/list-editor.svelte
+++ b/src/lib/components/list-editor/list-editor.svelte
@@ -62,6 +62,11 @@
   export let blockInteraction = false;
   export let addOnMount: string | undefined = undefined;
 
+  /**
+   * Pass an array of keys for items which the user will not be able to add to the list.
+   */
+  export let blockedKeys: string[] = [];
+
   $: selectedPercentages = Object.fromEntries(
     Object.entries(percentages).filter(([slug]) => selected.includes(slug)),
   );
@@ -90,6 +95,8 @@
       let gitProject = await gitProjectService.getByUrl(inputValue);
 
       const id = gitProject.source.url;
+      if (blockedKeys.includes(id)) throw new Error('Project ID is already used');
+
       // Prevent duplicates.
       if (selected.indexOf(id) === -1) {
         items[id] = projectItem(gitProject);
@@ -124,6 +131,8 @@
         : await ensStore.reverseLookup(inputValue);
       assert(address);
 
+      if (blockedKeys.includes(address)) throw new Error('This address is already used');
+
       if (items[address]) {
         isAddingProject = false;
         return;
diff --git a/src/lib/flows/edit-project-splits/steps/edit-dependency-list.svelte b/src/lib/flows/edit-project-splits/steps/edit-dependency-list.svelte
index e6d5c259f..cddbff14c 100644
--- a/src/lib/flows/edit-project-splits/steps/edit-dependency-list.svelte
+++ b/src/lib/flows/edit-project-splits/steps/edit-dependency-list.svelte
@@ -27,6 +27,7 @@
     bind:percentages={$context.dependencySplits.percentages}
     bind:items={$context.dependencySplits.items}
     bind:valid={formValid}
+    blockedKeys={$context.maintainerSplits.selected}
   />
   <svelte:fragment slot="actions">
     <Button
diff --git a/src/lib/flows/edit-project-splits/steps/edit-maintainer-list.svelte b/src/lib/flows/edit-project-splits/steps/edit-maintainer-list.svelte
index f50dd5a1c..63786391a 100644
--- a/src/lib/flows/edit-project-splits/steps/edit-maintainer-list.svelte
+++ b/src/lib/flows/edit-project-splits/steps/edit-maintainer-list.svelte
@@ -38,6 +38,7 @@
     bind:items={$context.maintainerSplits.items}
     bind:valid={formValid}
     allowedItems="eth-addresses"
+    blockedKeys={$context.dependencySplits.selected}
   />
   <svelte:fragment slot="actions">
     <Button disabled={!formValid} icon={ArrowRight} variant="primary" on:click={nextStep}
diff --git a/src/routes/app/(flows)/claim-project/steps/configure-dependencies/configure-dependencies.svelte b/src/routes/app/(flows)/claim-project/steps/configure-dependencies/configure-dependencies.svelte
index e13af1e35..150c2d1bc 100644
--- a/src/routes/app/(flows)/claim-project/steps/configure-dependencies/configure-dependencies.svelte
+++ b/src/routes/app/(flows)/claim-project/steps/configure-dependencies/configure-dependencies.svelte
@@ -73,6 +73,7 @@
     bind:percentages={$context.dependencySplits.percentages}
     bind:items={$context.dependencySplits.items}
     bind:valid={formValid}
+    blockedKeys={$context.maintainerSplits.selected}
     maxItems={200 - countOfMaintainerSplits}
   />
   <svelte:fragment slot="left-actions">
diff --git a/src/routes/app/(flows)/claim-project/steps/configure-maintainers/configure-maintainers.svelte b/src/routes/app/(flows)/claim-project/steps/configure-maintainers/configure-maintainers.svelte
index 215513f31..6326012e4 100644
--- a/src/routes/app/(flows)/claim-project/steps/configure-maintainers/configure-maintainers.svelte
+++ b/src/routes/app/(flows)/claim-project/steps/configure-maintainers/configure-maintainers.svelte
@@ -37,6 +37,7 @@
     bind:valid={formValid}
     maxItems={200 - countOfDependencySplits}
     allowedItems="eth-addresses"
+    blockedKeys={$context.dependencySplits.selected}
   />
   <svelte:fragment slot="left-actions">
     <Button icon={ArrowLeftIcon} on:click={() => dispatch('goBackward')}>Go back</Button>