diff --git a/app/src/main/java/org/searchmob/ui/settings/SettingsViewModel.kt b/app/src/main/java/org/searchmob/ui/settings/SettingsViewModel.kt
index 1c46fa4..6cc402b 100644
--- a/app/src/main/java/org/searchmob/ui/settings/SettingsViewModel.kt
+++ b/app/src/main/java/org/searchmob/ui/settings/SettingsViewModel.kt
@@ -227,14 +227,28 @@ class SettingsViewModel(
         viewModelScope.launch { preferences.setDynamicColor(enabled) }
     }
 
-    /** Set the named theme for the light slot (light-mode themes only). Persists immediately. */
+    /**
+     * Set the named theme for the light slot (light-mode themes only). Persists immediately.
+     * Picking a theme is an explicit choice to use it, so Material You (which overrides the named
+     * themes while it is on) is switched off in the same edit; otherwise the pick appears to do
+     * nothing until the user finds the toggle.
+     */
     fun setLightTheme(themeId: String) {
-        viewModelScope.launch { preferences.setLightTheme(themeId) }
+        viewModelScope.launch {
+            preferences.setDynamicColor(false)
+            preferences.setLightTheme(themeId)
+        }
     }
 
-    /** Set the named theme for the dark slot (dark-mode themes only). Persists immediately. */
+    /**
+     * Set the named theme for the dark slot (dark-mode themes only). Persists immediately.
+     * Switches Material You off for the same reason as [setLightTheme].
+     */
     fun setDarkTheme(themeId: String) {
-        viewModelScope.launch { preferences.setDarkTheme(themeId) }
+        viewModelScope.launch {
+            preferences.setDynamicColor(false)
+            preferences.setDarkTheme(themeId)
+        }
     }
 
     /** Set the base UI font size in points; clamped to the supported range by the repository. */
diff --git a/app/src/test/java/org/searchmob/ui/settings/SettingsViewModelThemeTest.kt b/app/src/test/java/org/searchmob/ui/settings/SettingsViewModelThemeTest.kt
new file mode 100644
index 0000000..9804d1a
--- /dev/null
+++ b/app/src/test/java/org/searchmob/ui/settings/SettingsViewModelThemeTest.kt
@@ -0,0 +1,83 @@
+package org.searchmob.ui.settings
+
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import org.searchmob.data.history.InMemoryHistoryStore
+import org.searchmob.ui.prefs.InMemoryPreferencesStore
+import org.searchmob.ui.prefs.PreferencesRepository
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class SettingsViewModelThemeTest {
+    private val dispatcher = StandardTestDispatcher()
+    private lateinit var preferences: PreferencesRepository
+    private lateinit var viewModel: SettingsViewModel
+
+    @Before
+    fun setUp() {
+        Dispatchers.setMain(dispatcher)
+        preferences = PreferencesRepository(InMemoryPreferencesStore())
+        viewModel =
+            SettingsViewModel(
+                preferences = preferences,
+                historyStore = InMemoryHistoryStore(),
+                engineCatalog = emptyList(),
+                engineEnabledSink = MutableStateFlow(emptyMap()),
+                apiKeysSink = MutableStateFlow(emptyMap()),
+            )
+    }
+
+    @After
+    fun tearDown() {
+        Dispatchers.resetMain()
+    }
+
+    @Test
+    fun `picking a light theme switches Material You off so the pick takes effect`() =
+        runTest(dispatcher) {
+            assertTrue(preferences.preferences.first().dynamicColor) // default on
+
+            viewModel.setLightTheme("github-light")
+            advanceUntilIdle()
+
+            val prefs = preferences.preferences.first()
+            assertEquals("github-light", prefs.lightThemeId)
+            assertFalse(prefs.dynamicColor)
+        }
+
+    @Test
+    fun `picking a dark theme switches Material You off so the pick takes effect`() =
+        runTest(dispatcher) {
+            viewModel.setDarkTheme("dracula")
+            advanceUntilIdle()
+
+            val prefs = preferences.preferences.first()
+            assertEquals("dracula", prefs.darkThemeId)
+            assertFalse(prefs.dynamicColor)
+        }
+
+    @Test
+    fun `re-enabling Material You after a pick is respected`() =
+        runTest(dispatcher) {
+            viewModel.setDarkTheme("dracula")
+            advanceUntilIdle()
+            viewModel.setDynamicColor(true)
+            advanceUntilIdle()
+
+            val prefs = preferences.preferences.first()
+            assertTrue(prefs.dynamicColor)
+            assertEquals("dracula", prefs.darkThemeId) // the slot choice is kept
+        }
+}