diff --git a/iris/android-app/build-apk.sh b/iris/android-app/build-apk.sh
index c4073da..7da862f 100755
--- a/iris/android-app/build-apk.sh
+++ b/iris/android-app/build-apk.sh
@@ -52,6 +52,11 @@ if [ -z "$NDK_DIR" ]; then
 fi
 export ANDROID_NDK_HOME="$NDK_DIR"
 
+# Only the ABI asked for goes into the APK. cargo ndk adds its output beside
+# whatever earlier builds left here, and Gradle packages every directory it
+# finds -- a debug x86_64 emulator build left behind made an arm64 "release"
+# 339 MB on 2026-09-06.
+rm -rf app/src/main/jniLibs
 echo "build-apk.sh: cargo ndk -t $ABI build ${BUILD_TYPE:+(${BUILD_TYPE})} --features \"$FEATURES\""
 if [ "$BUILD_TYPE" = "release" ]; then
     cargo ndk -t "$ABI" -P 26 -o app/src/main/jniLibs/ build --release --features "$FEATURES"