diff --git a/WordPressUtils/src/androidTest/java/org/wordpress/android/util/PhotonUtilsTest.java b/WordPressUtils/src/androidTest/java/org/wordpress/android/util/PhotonUtilsTest.java
index 0e2d4b301..c6f3ee743 100644
--- a/WordPressUtils/src/androidTest/java/org/wordpress/android/util/PhotonUtilsTest.java
+++ b/WordPressUtils/src/androidTest/java/org/wordpress/android/util/PhotonUtilsTest.java
@@ -103,4 +103,12 @@ public void getPhotonImageUrlUsesSslOnHttpsImageUrl() {
 
         assertThat(photonUrl, equalTo("https://i0.wp.com/mysite.com/test.jpg?strip=info&quality=65&resize=2,1&ssl=1"));
     }
+
+    @Test
+    public void getPhotonImageUrlWithErroneousSchemePosition() {
+        String imageUrl = "mysite.com/test.jpg#http://another.com";
+        String photonUrl = PhotonUtils.getPhotonImageUrl(imageUrl, 1, 1);
+
+        assertThat(photonUrl, equalTo(imageUrl));
+    }
 }
diff --git a/WordPressUtils/src/main/java/org/wordpress/android/util/PhotonUtils.java b/WordPressUtils/src/main/java/org/wordpress/android/util/PhotonUtils.java
index 2f12eb05f..e54d346f8 100644
--- a/WordPressUtils/src/main/java/org/wordpress/android/util/PhotonUtils.java
+++ b/WordPressUtils/src/main/java/org/wordpress/android/util/PhotonUtils.java
@@ -52,6 +52,8 @@ public static String getPhotonImageUrl(String imageUrl, int width, int height, Q
             return "";
         }
 
+        String originalUrl = imageUrl;
+
         // make sure it's valid
         int schemePos = imageUrl.indexOf("://");
         if (schemePos == -1) {
@@ -138,6 +140,12 @@ public static String getPhotonImageUrl(String imageUrl, int width, int height, Q
             query += "&ssl=1";
         }
 
-        return "https://i0.wp.com/" + imageUrl.substring(schemePos + 3, imageUrl.length()) + query;
+        int beginIndex = schemePos + 3;
+        if (beginIndex < 0 || beginIndex > imageUrl.length()) {
+            // Fallback to original URL if the beginIndex is invalid to avoid `StringIndexOutOfBoundsException`
+            // Ref: https://github.com/wordpress-mobile/WordPress-Android/issues/18626
+            return originalUrl;
+        }
+        return "https://i0.wp.com/" + imageUrl.substring(beginIndex) + query;
     }
 }