sivefunc · Oct 10, 2026
diff --git a/...act-native/ReactAndroid/src/main/java/com/facebook/react/views/text/TextAttributeProps.kt b/...act-native/ReactAndroid/src/main/java/com/facebook/react/views/text/TextAttributeProps.kt
@@ -40,7 +40,8 @@ public class TextAttributeProps private constructor() {
           if (value == ReactConstants.UNSET.toFloat()) {
             Float.NaN
           } else {
-            if (allowFontScaling) toPixelFromSP(value) else toPixelFromDIP(value)
+            if (allowFontScaling) toPixelFromSP(value, maxFontSizeMultiplier)
+            else toPixelFromDIP(value)
           }
     }
 
@@ -169,7 +170,7 @@ public class TextAttributeProps private constructor() {
   public var letterSpacing: Float
     get() {
       val letterSpacingPixels =
-          if (allowFontScaling) toPixelFromSP(letterSpacingInput)
+          if (allowFontScaling) toPixelFromSP(letterSpacingInput, maxFontSizeMultiplier)
           else toPixelFromDIP(letterSpacingInput)
 
       require(fontSize > 0) { "FontSize should be a positive value. Current value: $fontSize" }

diff --git a/...native/ReactAndroid/src/test/java/com/facebook/react/views/text/TextAttributePropsTest.kt b/...native/ReactAndroid/src/test/java/com/facebook/react/views/text/TextAttributePropsTest.kt
@@ -5,13 +5,18 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+@file:Suppress("DEPRECATION") // DisplayMetrics.scaledDensity, to simulate a system font scale
+
 package com.facebook.react.views.text
 
+import android.util.DisplayMetrics
 import android.view.Gravity
 import com.facebook.react.bridge.JavaOnlyMap
+import com.facebook.react.common.mapbuffer.WritableMapBuffer
 import com.facebook.react.uimanager.DisplayMetricsHolder
 import com.facebook.react.uimanager.ReactStylesDiffMap
 import org.assertj.core.api.Assertions.assertThat
+import org.assertj.core.api.Assertions.within
 import org.junit.After
 import org.junit.Before
 import org.junit.Test
@@ -84,11 +89,133 @@ class TextAttributePropsTest {
     assertThat(textAlignment("end", isRTL = true)).isEqualTo(Gravity.LEFT)
   }
 
+  @Test
+  fun lineHeightIsCappedByMaxFontSizeMultiplier() {
+    setFontScale(2f)
+
+    val textAttributes =
+        TextAttributeProps.fromReadableMap(
+            ReactStylesDiffMap(
+                JavaOnlyMap.of("fontSize", 14.0, "lineHeight", 20.0, "maxFontSizeMultiplier", 1.3)
+            ),
+        )
+
+    assertThat(textAttributes.lineHeight).isCloseTo(20f * DENSITY * 1.3f, within(0.001f))
+  }
+
+  @Test
+  fun lineHeightIsCappedByMaxFontSizeMultiplierFromMapBuffer() {
+    setFontScale(2f)
+
+    // Keys are iterated in ascending order, so lineHeight is set before maxFontSizeMultiplier.
+    val textAttributes =
+        TextAttributeProps.fromMapBuffer(
+            WritableMapBuffer()
+                .put(TextAttributeProps.TA_KEY_FONT_SIZE, 14.0)
+                .put(TextAttributeProps.TA_KEY_LINE_HEIGHT, 20.0)
+                .put(TextAttributeProps.TA_KEY_MAX_FONT_SIZE_MULTIPLIER, 1.3),
+        )
+
+    assertThat(textAttributes.lineHeight).isCloseTo(20f * DENSITY * 1.3f, within(0.001f))
+  }
+
+  @Test
+  fun letterSpacingIsCappedByMaxFontSizeMultiplier() {
+    setFontScale(2f)
+
+    val textAttributes =
+        TextAttributeProps.fromReadableMap(
+            ReactStylesDiffMap(
+                JavaOnlyMap.of("fontSize", 14.0, "letterSpacing", 2.0, "maxFontSizeMultiplier", 1.3)
+            ),
+        )
+
+    assertThat(textAttributes.fontSize).isEqualTo(37) // ceil(14 * 2 * 1.3)
+    assertThat(textAttributes.letterSpacing)
+        .isCloseTo(2f * DENSITY * 1.3f / textAttributes.fontSize, within(0.001f))
+  }
+
+  @Test
+  fun lineHeightScalesWithFontScaleWithoutMaxFontSizeMultiplier() {
+    setFontScale(2f)
+
+    val textAttributes =
+        TextAttributeProps.fromReadableMap(
+            ReactStylesDiffMap(JavaOnlyMap.of("fontSize", 14.0, "lineHeight", 20.0)),
+        )
+
+    assertThat(textAttributes.lineHeight).isCloseTo(20f * DENSITY * 2f, within(0.001f))
+  }
+
+  @Test
+  fun lineHeightIsNotCappedWhenFontScaleIsBelowMaxFontSizeMultiplier() {
+    setFontScale(1.2f)
+
+    val textAttributes =
+        TextAttributeProps.fromReadableMap(
+            ReactStylesDiffMap(
+                JavaOnlyMap.of("fontSize", 14.0, "lineHeight", 20.0, "maxFontSizeMultiplier", 1.5)
+            ),
+        )
+
+    assertThat(textAttributes.lineHeight).isCloseTo(20f * DENSITY * 1.2f, within(0.001f))
+  }
+
+  @Test
+  fun lineHeightIsNotCappedWhenMaxFontSizeMultiplierIsZero() {
+    setFontScale(2f)
+
+    val textAttributes =
+        TextAttributeProps.fromReadableMap(
+            ReactStylesDiffMap(
+                JavaOnlyMap.of("fontSize", 14.0, "lineHeight", 20.0, "maxFontSizeMultiplier", 0.0)
+            ),
+        )
+
+    assertThat(textAttributes.lineHeight).isCloseTo(20f * DENSITY * 2f, within(0.001f))
+  }
+
+  @Test
+  fun lineHeightIgnoresFontScaleWhenFontScalingIsDisabled() {
+    setFontScale(2f)
+
+    val textAttributes =
+        TextAttributeProps.fromReadableMap(
+            ReactStylesDiffMap(
+                JavaOnlyMap.of(
+                    "fontSize",
+                    14.0,
+                    "lineHeight",
+                    20.0,
+                    "maxFontSizeMultiplier",
+                    1.3,
+                    "allowFontScaling",
+                    false,
+                )
+            ),
+        )
+
+    assertThat(textAttributes.lineHeight).isCloseTo(20f * DENSITY, within(0.001f))
+  }
+
+  private fun setFontScale(fontScale: Float) {
+    DisplayMetricsHolder.setScreenDisplayMetrics(
+        DisplayMetrics().apply {
+          density = DENSITY
+          scaledDensity = DENSITY * fontScale
+        },
+    )
+  }
+
   private fun textAlignment(textAlign: String, isRTL: Boolean): Int {
     return TextAttributeProps.getTextAlignment(
         ReactStylesDiffMap(JavaOnlyMap.of("textAlign", textAlign)),
         isRTL,
         Gravity.CENTER_HORIZONTAL,
     )
   }
+
+  private companion object {
+    const val DENSITY = 2f
+  }
 }
diff --git a/packages/rn-tester/js/examples/Text/TextExample.android.js b/packages/rn-tester/js/examples/Text/TextExample.android.js
@@ -531,6 +531,18 @@ function MaxFontSizeMultiplierExample(props: {}): React.Node {
       <Text allowFontScaling={true} maxFontSizeMultiplier={1}>
         <Text maxFontSizeMultiplier={0}>Ignore inherited max (no max)</Text>
       </Text>
+      <Text
+        allowFontScaling={true}
+        maxFontSizeMultiplier={1}
+        style={{
+          marginTop: 10,
+          lineHeight: 20,
+          letterSpacing: 1,
+          backgroundColor: 'lightgray',
+        }}>
+        lineHeight and letterSpacing are capped too (max 1x): these lines keep
+        the same spacing at any system font size
+      </Text>
     </View>
   );
 }

diff --git a/packages/rn-tester/js/examples/Text/TextExample.ios.js b/packages/rn-tester/js/examples/Text/TextExample.ios.js
@@ -1269,6 +1269,18 @@ const examples = [
           <Text allowFontScaling={true} maxFontSizeMultiplier={1}>
             <Text maxFontSizeMultiplier={0}>Ignore inherited max (no max)</Text>
           </Text>
+          <Text
+            allowFontScaling={true}
+            maxFontSizeMultiplier={1}
+            style={{
+              marginTop: 10,
+              lineHeight: 20,
+              letterSpacing: 1,
+              backgroundColor: 'lightgray',
+            }}>
+            lineHeight and letterSpacing are capped too (max 1x): these lines
+            keep the same spacing at any system font size
+          </Text>
           <Text
             allowFontScaling={true}
             style={{fontSize: 22}}