diff --git a/CHANGELOG.md b/CHANGELOG.md
index 35c58b7539..466c172b57 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,8 +25,8 @@ All notable changes to this project will be documented in this file. Take a look
 ### Changed
 
 * Readium resources are now prefixed with `readium_`. Take care of updating any overridden resource by following [the migration guide](docs/migration-guide.md#300).
-* `Link` and `Locator`'s `href` do not start with a `/` for packaged publications anymore.
-    * To ensure backward-compatibility, `href` starting with a `/` are still supported. But you may want to update the locators persisted in your database to drop the `/` prefix for packaged publications.
+* `Link` and `Locator`'s `href` are normalized as valid URLs to improve interoperability with the Readium Web toolkits.
+    * **You MUST migrate your database if you were persisting HREF and Locators**. Take a look at [the migration guide](docs/migration-guide.md) for guidance.
 
 #### Shared
 
diff --git a/docs/migration-guide.md b/docs/migration-guide.md
index a6fb823fd3..e76397d074 100644
--- a/docs/migration-guide.md
+++ b/docs/migration-guide.md
@@ -29,6 +29,62 @@ dependencies {
 }
 ```
 
+### Migration of HREFs (bookmarks, annotations, etc.)
+
+:warning: This requires a database migration in your application, if you were persisting `Locator` objects.
+
+In Readium v2.x, a `Link` or `Locator`'s `href` could be either:
+
+* a full valid URL for a streamed publication, e.g. `https://domain.com/isbn/dir/my%20chapter.html`,
+* a percent-decoded path for a local archive such as an EPUB, e.g. `/dir/my chapter.html`.
+    * Note that it was relative to the root of the archive (`/`).
+
+To improve the interoperability with other Readium toolkits – in particular the Readium Web Toolkits, which only work in a streaming context – **Readium v3 now generates and expects valid URLs** for `Locator` and `Link`'s `href`.
+
+* `https://domain.com/isbn/dir/my%20chapter.html` is left unchanged, as it already a valid URL.
+* `/dir/my chapter.html` becomes the relative URL path `dir/my%20chapter.html`
+    * We dropped the `/` prefix to avoid issues with resolving to a base URL.
+    * Special characters are percent-encoded.
+    
+**You must migrate the HREFs or Locators stored in your database** when upgrading to Readium 3.
+
+To assist you in migrating your data, two helpers are provided: `Url.fromLegacyHref()` and `Locator.fromJSON(withLegacyHref)`:
+
+```kotlin
+val href = Url.fromLegacyHref(legacyHref)?.toString()
+val locator = Locator.fromJSON(legacyJSON, withLegacyHref = true)
+```
+
+Here's a sample Jetpack Room migration that you can use as inspiration:
+
+```kotlin
+val MIGRATION_HREF = object : Migration(1, 2) {
+
+    override fun migrate(db: SupportSQLiteDatabase) {
+        val normalizedHrefs: Map<Long, String> = buildMap {
+            db.query("SELECT id, href FROM bookmarks").use { cursor ->
+                while (cursor.moveToNext()) {
+                    val id = cursor.getLong(0)
+                    val href = cursor.getString(1)
+
+                    val normalizedHref = Url.fromLegacyHref(href)?.toString()
+                    if (normalizedHref != null) {
+                        put(id, normalizedHref)
+                    }
+                }
+            }
+        }
+
+        val stmt = db.compileStatement("UPDATE bookmarks SET href = ? WHERE id = ?")
+        for ((id, href) in normalizedHrefs) {
+            stmt.bindString(1, href)
+            stmt.bindLong(2, id)
+            stmt.executeUpdateDelete()
+        }
+    }
+}
+```
+
 ### All resources now have the prefix `readium_`.
 
 To avoid conflicts when merging your app resources, all resources declared in the Readium toolkit now have the prefix `readium_`. This means that you must rename any layouts or strings you have overridden. Here is a comprehensive list of the changes.
diff --git a/readium/shared/src/main/java/org/readium/r2/shared/publication/Locator.kt b/readium/shared/src/main/java/org/readium/r2/shared/publication/Locator.kt
index 556f182db1..7bf5325930 100644
--- a/readium/shared/src/main/java/org/readium/r2/shared/publication/Locator.kt
+++ b/readium/shared/src/main/java/org/readium/r2/shared/publication/Locator.kt
@@ -200,7 +200,8 @@ public data class Locator(
         public fun fromJSON(
             json: JSONObject?,
             mediaTypeRetriever: MediaTypeRetriever = MediaTypeRetriever(),
-            warnings: WarningLogger? = null
+            warnings: WarningLogger? = null,
+            withLegacyHref: Boolean = false
         ): Locator? {
             val href = json?.optNullableString("href")
             val type = json?.optNullableString("type")
@@ -209,7 +210,10 @@ public data class Locator(
                 return null
             }
 
-            val url = Url(href) ?: run {
+            val url = (
+                if (withLegacyHref) Url.fromLegacyHref(href)
+                else Url(href)
+            ) ?: run {
                 warnings?.log(Locator::class.java, "[href] is not a valid URL", json)
                 return null
             }
diff --git a/readium/shared/src/test/java/org/readium/r2/shared/publication/LocatorTest.kt b/readium/shared/src/test/java/org/readium/r2/shared/publication/LocatorTest.kt
index 846905d0eb..e197f3daf8 100644
--- a/readium/shared/src/test/java/org/readium/r2/shared/publication/LocatorTest.kt
+++ b/readium/shared/src/test/java/org/readium/r2/shared/publication/LocatorTest.kt
@@ -71,6 +71,23 @@ class LocatorTest {
         assertNull(Locator.fromJSON(JSONObject("{ 'invalid': 'object' }")))
     }
 
+    @Test fun `parse {Locator} with legacy HREF`() {
+        val json = JSONObject("""
+            {
+                "href": "legacy href",
+                "type": "text/html"
+            }
+        """)
+
+        assertNull(Locator.fromJSON(json))
+        assertNull(Locator.fromJSON(json, withLegacyHref = false))
+
+        assertEquals(
+            Locator(href = Url("legacy%20href")!!, mediaType = MediaType.HTML),
+            Locator.fromJSON(json, withLegacyHref = true)
+        )
+    }
+
     @Test fun `get {Locator} minimal JSON`() {
         assertJSONEquals(
             JSONObject(