diff --git a/CHANGELOG.md b/CHANGELOG.md
index c45abc3207..cc5d814d1e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,15 @@ All notable changes to this project will be documented in this file. Take a look
 
 **Warning:** Features marked as *experimental* may change or be removed in a future release without notice. Use with caution.
 
-<!--## [Unreleased]-->
+## [Unreleased]
+
+### Added
+
+#### Navigator
+
+* New `EPUBNavigatorFragment.Configuration.useReadiumCssFontSize` option to revert to the 2.2.0 strategy for setting the font size of reflowable EPUB publications.
+    * The native font size strategy introduced in 2.3.0 uses the Android web view's [`WebSettings.textZoom`](https://developer.android.com/reference/android/webkit/WebSettings#setTextZoom(int)) property to adjust the font size. 2.2.0 was using Readium CSS's [`--USER__fontSize` variable](https://readium.org/readium-css/docs/CSS12-user_prefs.html#font-size).
+    * `WebSettings.textZoom` will work with more publications than `--USER__fontSize`, even the ones poorly authored. However the page width is not adjusted when changing the font size to keep the optimal line length.
 
 ## [2.3.0]
 
diff --git a/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorFragment.kt b/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorFragment.kt
index 5ebca0739f..a449880996 100644
--- a/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorFragment.kt
+++ b/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorFragment.kt
@@ -86,7 +86,7 @@ typealias JavascriptInterfaceFactory = (resource: Link) -> Any?
  *
  * To use this [Fragment], create a factory with `EpubNavigatorFragment.createFactory()`.
  */
-@OptIn(ExperimentalDecorator::class, ExperimentalReadiumApi::class)
+@OptIn(ExperimentalDecorator::class, ExperimentalReadiumApi::class, DelicateReadiumApi::class)
 class EpubNavigatorFragment internal constructor(
     override val publication: Publication,
     private val baseUrl: String?,
@@ -132,6 +132,22 @@ class EpubNavigatorFragment internal constructor(
         @ExperimentalReadiumApi
         var readiumCssRsProperties: RsProperties,
 
+        /**
+         * When disabled, the Android web view's `WebSettings.textZoom` will be used to adjust the
+         * font size, instead of using the Readium CSS's `--USER__fontSize` variable.
+         *
+         * `WebSettings.textZoom` will work with more publications than `--USER__fontSize`, even the
+         * ones poorly authored. However, the page width is not adjusted when changing the font
+         * size to keep the optimal line length.
+         *
+         * See:
+         *   - https://github.com/readium/mobile/issues/5
+         *   - https://github.com/readium/mobile/issues/1#issuecomment-652431984
+         */
+        @ExperimentalReadiumApi
+        @DelicateReadiumApi
+        var useReadiumCssFontSize: Boolean = true,
+
         /**
          * Supported HTML decoration templates.
          */
@@ -503,18 +519,20 @@ class EpubNavigatorFragment internal constructor(
     }
 
     private fun R2PagerAdapter.setFontSize(fontSize: Double) {
-        r2PagerAdapter?.mFragments?.forEach { _, fragment ->
+        if (config.useReadiumCssFontSize) return
+
+        mFragments.forEach { _, fragment ->
             (fragment as? R2EpubPageFragment)?.setFontSize(fontSize)
         }
     }
 
     private inner class PagerAdapterListener : R2PagerAdapter.Listener {
         override fun onCreatePageFragment(fragment: Fragment) {
-            if (viewModel.layout == EpubLayout.FIXED) {
-                return
+            if (viewModel.layout == EpubLayout.REFLOWABLE) {
+                if (!config.useReadiumCssFontSize) {
+                    (fragment as? R2EpubPageFragment)?.setFontSize(settings.value.fontSize)
+                }
             }
-
-            (fragment as? R2EpubPageFragment)?.setFontSize(settings.value.fontSize)
         }
     }
 
diff --git a/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorViewModel.kt b/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorViewModel.kt
index 06848d4905..9ce65e2f86 100644
--- a/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorViewModel.kt
+++ b/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubNavigatorViewModel.kt
@@ -30,6 +30,7 @@ import org.readium.r2.navigator.html.HtmlDecorationTemplates
 import org.readium.r2.navigator.preferences.*
 import org.readium.r2.navigator.util.createViewModelFactory
 import org.readium.r2.shared.COLUMN_COUNT_REF
+import org.readium.r2.shared.DelicateReadiumApi
 import org.readium.r2.shared.ExperimentalReadiumApi
 import org.readium.r2.shared.SCROLL_REF
 import org.readium.r2.shared.extensions.addPrefix
@@ -44,7 +45,7 @@ internal enum class DualPage {
     AUTO, OFF, ON
 }
 
-@OptIn(ExperimentalReadiumApi::class, ExperimentalDecorator::class)
+@OptIn(ExperimentalReadiumApi::class, ExperimentalDecorator::class, DelicateReadiumApi::class)
 internal class EpubNavigatorViewModel(
     application: Application,
     val publication: Publication,
@@ -118,7 +119,7 @@ internal class EpubNavigatorViewModel(
             fontFamilyDeclarations = config.fontFamilyDeclarations,
             googleFonts = googleFonts,
             assetsBaseHref = WebViewServer.assetsBaseHref
-        ).update(settings.value)
+        ).update(settings.value, useReadiumCssFontSize = config.useReadiumCssFontSize)
     )
 
     init {
@@ -230,7 +231,7 @@ internal class EpubNavigatorViewModel(
 
         val newSettings = settingsPolicy.settings(preferences)
         _settings.value = newSettings
-        css.update { it.update(newSettings) }
+        css.update { it.update(newSettings, useReadiumCssFontSize = config.useReadiumCssFontSize) }
 
         val needsInvalidation: Boolean = (
             oldSettings.readingProgression != newSettings.readingProgression ||
diff --git a/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubSettings.kt b/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubSettings.kt
index 1ba34459e9..f439ba1071 100644
--- a/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubSettings.kt
+++ b/readium/navigator/src/main/java/org/readium/r2/navigator/epub/EpubSettings.kt
@@ -65,7 +65,7 @@ data class EpubSettings(
 ) : Configurable.Settings
 
 @OptIn(ExperimentalReadiumApi::class)
-internal fun ReadiumCss.update(settings: EpubSettings): ReadiumCss {
+internal fun ReadiumCss.update(settings: EpubSettings, useReadiumCssFontSize: Boolean): ReadiumCss {
 
     fun resolveFontStack(fontFamily: String): List<String> = buildList {
         add(fontFamily)
@@ -109,9 +109,8 @@ internal fun ReadiumCss.update(settings: EpubSettings): ReadiumCss {
                 backgroundColor = backgroundColor?.toCss(),
                 fontOverride = (fontFamily != null || textNormalization),
                 fontFamily = fontFamily?.toCss(),
-                // Font size is handled natively with WebSettings.textZoom.
-                // See https://github.com/readium/mobile/issues/1#issuecomment-652431984
-//                fontSize = fontSize?.let { Length.Percent(it) },
+                fontSize = if (useReadiumCssFontSize) Length.Percent(fontSize)
+                else null,
                 advancedSettings = !publisherStyles,
                 typeScale = typeScale,
                 textAlign = when (textAlign) {