diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03bba5a..2ea1d26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## unreleased
 
 * Update browser-switch to 2.0.0-beta2
+* Run `onComplete` and `onCancel` callbacks after WebView window has loaded (fixes #26)
 
 ## 4.0.0-beta1
 
diff --git a/Demo/src/main/java/com/braintreepayments/popupbridge/demo/PopupActivity.java b/Demo/src/main/java/com/braintreepayments/popupbridge/demo/PopupActivity.java
index 44058e7..bc96783 100644
--- a/Demo/src/main/java/com/braintreepayments/popupbridge/demo/PopupActivity.java
+++ b/Demo/src/main/java/com/braintreepayments/popupbridge/demo/PopupActivity.java
@@ -5,10 +5,10 @@
 import android.os.Bundle;
 import android.webkit.WebView;
 
-import com.braintreepayments.api.PopupBridgeClient;
-
 import androidx.appcompat.app.AppCompatActivity;
 
+import com.braintreepayments.api.PopupBridgeClient;
+
 public class PopupActivity extends AppCompatActivity {
 
     private WebView mWebView;
diff --git a/PopupBridge/src/main/java/com/braintreepayments/api/PopupBridgeClient.java b/PopupBridge/src/main/java/com/braintreepayments/api/PopupBridgeClient.java
index b51ae65..2b9a154 100644
--- a/PopupBridge/src/main/java/com/braintreepayments/api/PopupBridgeClient.java
+++ b/PopupBridge/src/main/java/com/braintreepayments/api/PopupBridgeClient.java
@@ -104,10 +104,20 @@ private void onBrowserSwitchResult(BrowserSwitchResult result) {
         Uri returnUri = result.getDeepLinkUrl();
         if (result.getStatus() == BrowserSwitchStatus.CANCELED) {
             runJavaScriptInWebView(""
-                + "if (typeof window.popupBridge.onCancel === 'function') {"
-                + "  window.popupBridge.onCancel();"
+                + "function notifyCanceled() {"
+                + "  if (typeof window.popupBridge.onCancel === 'function') {"
+                + "    window.popupBridge.onCancel();"
+                + "  } else {"
+                + "    window.popupBridge.onComplete(null, null);"
+                + "  }"
+                + "}"
+                + ""
+                + "if (document.readyState === 'complete') {"
+                + "  notifyCanceled();"
                 + "} else {"
-                + "  window.popupBridge.onComplete(null, null);"
+                + "  window.addEventListener('load', function () {"
+                + "    notifyCanceled();"
+                + "  });"
                 + "}");
             return;
         } else if (result.getStatus() == BrowserSwitchStatus.SUCCESS) {
@@ -140,7 +150,20 @@ private void onBrowserSwitchResult(BrowserSwitchResult result) {
             payload = json.toString();
         }
 
-        runJavaScriptInWebView(String.format("window.popupBridge.onComplete(%s, %s);", error, payload));
+        String successJavascript = String.format(""
+            + "function notifyComplete() {"
+            + "  window.popupBridge.onComplete(%s, %s);"
+            + "}"
+            + ""
+            + "if (document.readyState === 'complete') {"
+            + "  notifyComplete();"
+            + "} else {"
+            + "  window.addEventListener('load', function () {"
+            + "    notifyComplete();"
+            + "  });"
+            + "}", error, payload);
+
+        runJavaScriptInWebView(successJavascript);
     }
 
     @JavascriptInterface
diff --git a/PopupBridge/src/test/java/com/braintreepayments/api/MockWebView.java b/PopupBridge/src/test/java/com/braintreepayments/api/MockWebView.java
index 82d0403..683f1af 100644
--- a/PopupBridge/src/test/java/com/braintreepayments/api/MockWebView.java
+++ b/PopupBridge/src/test/java/com/braintreepayments/api/MockWebView.java
@@ -19,7 +19,9 @@ public MockWebView(Context context) {
 
     @Override
     public void evaluateJavascript(String script, ValueCallback<String> resultCallback) {
-        String expression = "window\\.popupBridge\\.onComplete\\((.*), (.*)\\)";
+        // match everything except semi-colon to capture each parameter as a whole
+        // without drifting into other lines
+        String expression = "window\\.popupBridge\\.onComplete\\(([^;]*), ([^;]*)\\);";
         mJavascriptEval = script;
         Pattern pattern = Pattern.compile(expression);
         Matcher match = pattern.matcher(script);
diff --git a/PopupBridge/src/test/java/com/braintreepayments/api/PopupBridgeClientUnitTest.java b/PopupBridge/src/test/java/com/braintreepayments/api/PopupBridgeClientUnitTest.java
index c1e9e76..e7aa159 100644
--- a/PopupBridge/src/test/java/com/braintreepayments/api/PopupBridgeClientUnitTest.java
+++ b/PopupBridge/src/test/java/com/braintreepayments/api/PopupBridgeClientUnitTest.java
@@ -71,7 +71,7 @@ public void constructor_whenWebViewIsNull_throwsException() {
         try {
             new PopupBridgeClient(fragmentActivity, null, "my-custom-url-scheme");
             fail("Should throw");
-        } catch (IllegalArgumentException e){
+        } catch (IllegalArgumentException e) {
             assertEquals(e.getMessage(), "WebView is null");
         }
     }
@@ -190,7 +190,7 @@ public void onBrowserSwitchResult_whenReturnUrlHasNoQueryParams_reportsPayloadWi
     }
 
     @Test
-    public void  onBrowserSwitchResult_whenReturnUrlIncludesFragmentIdentifier_reportsPayloadWithFragmentIdentifier()
+    public void onBrowserSwitchResult_whenReturnUrlIncludesFragmentIdentifier_reportsPayloadWithFragmentIdentifier()
             throws JSONException {
         BrowserSwitchResult result = mock(BrowserSwitchResult.class);
         when(result.getStatus()).thenReturn(BrowserSwitchStatus.SUCCESS);
@@ -242,8 +242,8 @@ public void onBrowserSwitchResult_whenNoPath_returnsEmptyString() throws JSONExc
         BrowserSwitchResult result = mock(BrowserSwitchResult.class);
         when(result.getStatus()).thenReturn(BrowserSwitchStatus.SUCCESS);
 
-         Uri uri = new Uri.Builder()
-                 .scheme("my-custom-url-scheme")
+        Uri uri = new Uri.Builder()
+                .scheme("my-custom-url-scheme")
                 .authority("popupbridgev1")
                 .build();
         when(result.getDeepLinkUrl()).thenReturn(uri);