diff --git a/README.md b/README.md
index 345baa3..bef2fd4 100644
--- a/README.md
+++ b/README.md
@@ -203,7 +203,7 @@ LinkForty.onDeepLink((url: string, data: DeepLinkData | null) => {
 
 ### `onDeferredDeepLink(callback)`
 
-Listen for deferred deep links. Called on first launch after install if the user clicked a LinkForty link before installing.
+Listen for deferred deep links. Called once, on the launch that reports the install: with the link's data if the user clicked a LinkForty link before installing, or `null` for an organic install. It can be registered before or after `init()`. Later launches don't call it; use `getInstallData()` for the install's link data.
 
 ```typescript
 LinkForty.onDeferredDeepLink((data: DeepLinkData | null) => {
diff --git a/__tests__/DeferredDeepLink.test.ts b/__tests__/DeferredDeepLink.test.ts
new file mode 100644
index 0000000..a0a6aa8
--- /dev/null
+++ b/__tests__/DeferredDeepLink.test.ts
@@ -0,0 +1,43 @@
+import { describe, it, expect, vi } from 'vitest';
+import { DeferredDeepLink } from '../src/DeferredDeepLink';
+import type { DeepLinkData } from '../src/types';
+
+const data = { shortCode: 'abc123', linkId: 'link-1' } as DeepLinkData;
+
+describe('DeferredDeepLink', () => {
+  it('calls a callback registered before the install is reported', () => {
+    const deferred = new DeferredDeepLink();
+    const callback = vi.fn();
+    deferred.register(callback);
+    deferred.deliver(data);
+
+    expect(callback).toHaveBeenCalledTimes(1);
+    expect(callback).toHaveBeenCalledWith(data);
+  });
+
+  it('calls a callback registered after the install is reported', () => {
+    const deferred = new DeferredDeepLink();
+    deferred.deliver(data);
+    const callback = vi.fn();
+    deferred.register(callback);
+
+    expect(callback).toHaveBeenCalledWith(data);
+  });
+
+  it('delivers null for an organic install registered after init', () => {
+    const deferred = new DeferredDeepLink();
+    deferred.deliver(null);
+    const callback = vi.fn();
+    deferred.register(callback);
+
+    expect(callback).toHaveBeenCalledWith(null);
+  });
+
+  it('calls nothing on a launch that does not report the install', () => {
+    const deferred = new DeferredDeepLink();
+    const callback = vi.fn();
+    deferred.register(callback);
+
+    expect(callback).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/DeferredDeepLink.ts b/src/DeferredDeepLink.ts
new file mode 100644
index 0000000..09effe9
--- /dev/null
+++ b/src/DeferredDeepLink.ts
@@ -0,0 +1,27 @@
+import type { DeepLinkData, DeferredDeepLinkCallback } from './types';
+
+/**
+ * Delivers the deferred deep link once, on the launch that reports the install:
+ * the link's data, or null for an organic install. A callback registered after
+ * that is called with the same result; on later launches nothing is delivered.
+ *
+ * Kept free of React Native imports so it can be tested (see urlParameters.ts).
+ */
+export class DeferredDeepLink {
+  private callback: DeferredDeepLinkCallback | null = null;
+  private delivered = false;
+  private data: DeepLinkData | null = null;
+
+  /** Registers the callback, replacing any earlier one. */
+  register(callback: DeferredDeepLinkCallback): void {
+    this.callback = callback;
+    if (this.delivered) callback(this.data);
+  }
+
+  /** Delivers the install's result. Called only on the launch that reports the install. */
+  deliver(data: DeepLinkData | null): void {
+    this.data = data;
+    this.delivered = true;
+    this.callback?.(data);
+  }
+}
diff --git a/src/LinkFortySDK.ts b/src/LinkFortySDK.ts
index ea92efd..503a179 100644
--- a/src/LinkFortySDK.ts
+++ b/src/LinkFortySDK.ts
@@ -8,6 +8,7 @@ import { DeepLinkHandler } from './DeepLinkHandler';
 import { AttributionContext } from './AttributionContext';
 import { NavigationTracker } from './NavigationTracker';
 import { LinkDomains } from './LinkDomains';
+import { DeferredDeepLink } from './DeferredDeepLink';
 import { SDK_NAME, SDK_VERSION } from './version';
 import type {
   LinkFortyConfig,
@@ -28,7 +29,8 @@ const STORAGE_KEYS = {
 export class LinkFortySDK {
   private config: LinkFortyConfig | null = null;
   private deepLinkHandler: DeepLinkHandler | null = null;
-  private deferredDeepLinkCallback: DeferredDeepLinkCallback | null = null;
+  /** Delivers the deferred deep link on the launch that reports the install */
+  private deferredDeepLink = new DeferredDeepLink();
   private installId: string | null = null;
   private externalUserId: string | null = null;
   private initialized: boolean = false;
@@ -165,17 +167,13 @@ export class LinkFortySDK {
   }
 
   /**
-   * Register callback for deferred deep links (new installs)
+   * Register callback for deferred deep links, called once on the launch that
+   * reports the install: with the link's data, or null for an organic install.
+   * Can be registered before or after init(). Later launches don't call it;
+   * use getInstallData() for the install's link data.
    */
   onDeferredDeepLink(callback: DeferredDeepLinkCallback): void {
-    this.deferredDeepLinkCallback = callback;
-
-    // If we already have install data, call the callback immediately
-    this.getInstallData().then((data) => {
-      if (data && this.deferredDeepLinkCallback) {
-        this.deferredDeepLinkCallback(data);
-      }
-    });
+    this.deferredDeepLink.register(callback);
   }
 
   /**
@@ -533,10 +531,7 @@ export class LinkFortySDK {
           await this.attribution.recordDeepLinkOpen(deepLinkData.linkId);
         }
 
-        // Call deferred deep link callback if registered
-        if (this.deferredDeepLinkCallback) {
-          this.deferredDeepLinkCallback(deepLinkData);
-        }
+        this.deferredDeepLink.deliver(deepLinkData);
 
         if (this.config.debug) {
           console.log('[LinkForty] Install attributed with confidence:', response.confidenceScore);
@@ -547,18 +542,14 @@ export class LinkFortySDK {
           console.log('[LinkForty] Install not attributed (organic install)');
         }
 
-        // Call callback with null to indicate organic install
-        if (this.deferredDeepLinkCallback) {
-          this.deferredDeepLinkCallback(null);
-        }
+        // null indicates an organic install
+        this.deferredDeepLink.deliver(null);
       }
     } catch (error) {
       console.error('[LinkForty] Failed to report install:', error);
 
-      // Call callback with null on error
-      if (this.deferredDeepLinkCallback) {
-        this.deferredDeepLinkCallback(null);
-      }
+      // null on error
+      this.deferredDeepLink.deliver(null);
     }
   }