diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f346aa0d82..3db05e8dfd 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -6,7 +6,13 @@ jobs:
   check:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4.1.7
+
+    - name: Set up JDK
+      uses: actions/setup-java@v4.2.1
+      with:
+        java-version: 17
+        distribution: temurin
 
     - name: Clone Flutter SDK
       # We can't do a depth-1 clone, because we need the most recent tag
diff --git a/android/app/build.gradle b/android/app/build.gradle
index 4a8b1eb783..529221630b 100644
--- a/android/app/build.gradle
+++ b/android/app/build.gradle
@@ -74,6 +74,16 @@ android {
     }
 }
 
+tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
+    // Compile Kotlin with `-Werror`... but only in release builds, so that it
+    // doesn't get in the way of quick local experiments for debugging.
+    //
+    // The string-searching makes this a bit of a mess, but it works.
+    // Better would be if we can add this to android.buildTypes.release above;
+    // but on a first attempt that didn't work (it affected debug builds too).
+    kotlinOptions.allWarningsAsErrors = name.contains("Release")
+}
+
 flutter {
     source '../..'
 }
diff --git a/tools/check b/tools/check
index 49df5cdc0a..3acb65a725 100755
--- a/tools/check
+++ b/tools/check
@@ -24,7 +24,12 @@ this_dir=${BASH_SOURCE[0]%/*}
 
 ## CLI PARSING
 
-default_suites=(analyze test build_runner drift pigeon icons)
+default_suites=(
+    analyze test
+    build_runner drift pigeon icons
+    android  # This takes multiple minutes in CI, so do it last.
+)
+
 extra_suites=(
     shellcheck  # Requires its own dependency, from outside the pub system.
 )
@@ -77,7 +82,7 @@ while (( $# )); do
         --all) opt_files=all; opt_all=1; shift;;
         --fix) opt_fix=1; shift;;
         --verbose) opt_verbose=1; shift;;
-        analyze|test|build_runner|drift|pigeon|icons|shellcheck)
+        analyze|test|build_runner|drift|pigeon|icons|android|shellcheck)
             opt_suites+=("$1"); shift;;
         *) usage;;
     esac
@@ -351,6 +356,18 @@ run_icons() {
     check_no_changes "icon updates" "${outputs[@]}"
 }
 
+run_android() {
+    # Omitted from this check:
+    #   pubspec.{yaml,lock} tools/check
+    files_check android/ \
+    || return 0
+
+    flutter build apk \
+    || return
+
+    flutter build appbundle
+}
+
 run_shellcheck() {
     # Omitted from this check: nothing (nothing known, anyway).
     files_check tools/ '!*.'{dart,js,json} \
@@ -424,6 +441,7 @@ for suite in "${opt_suites[@]}"; do
         drift)        run_drift ;;
         pigeon)       run_pigeon ;;
         icons)        run_icons ;;
+        android)      run_android ;;
         shellcheck)   run_shellcheck ;;
         *)            echo >&2 "Internal error: unknown suite $suite" ;;
     esac || failed+=( "$suite" )