diff --git a/scripts/build_android_apk.sh b/scripts/build_android_apk.sh
index 39c5119..1fc83ed 100755
--- a/scripts/build_android_apk.sh
+++ b/scripts/build_android_apk.sh
@@ -213,15 +213,35 @@ KEY_PASS="${KEY_PASS:-$KEYSTORE_PASS}"
 
 mkdir -p "$(dirname "$APK_OUT")"
 echo ">>> apksigner sign -> $APK_OUT"
+# Sign the schemes explicitly instead of relying on apksigner's auto behaviour.
+# Left to "auto", this pipeline produced an APK carrying invalid v1 (JAR)
+# signature files (META-INF/*.SF/.RSA present but failing v1 verification).
+# Android installs it fine via v2/v3, but Obtainium parses the APK's legacy v1
+# certificate at install time, gets an empty cert list, and crashes with
+# "RangeError (length): Invalid value: valid value range is empty: 0".
+# minSdk is 26 (solitaire_app/android/AndroidManifest.xml), so v1/JAR signing is
+# not needed at all — disable it and ship a clean v2+v3 signature, matching what
+# modern Android tooling produces for minSdk >= 24.
 "$BT/apksigner" sign \
   --ks "$KEYSTORE" \
   --ks-pass "pass:$KEYSTORE_PASS" \
   --ks-key-alias "$KEY_ALIAS" \
   --key-pass "pass:$KEY_PASS" \
+  --min-sdk-version 26 \
+  --v1-signing-enabled false \
+  --v2-signing-enabled true \
+  --v3-signing-enabled true \
   --out "$APK_OUT" \
   "$STAGING/app-aligned.apk"
 
 echo ">>> verify"
-"$BT/apksigner" verify --verbose "$APK_OUT"
+"$BT/apksigner" verify --min-sdk-version 26 --verbose "$APK_OUT"
+
+# Guard: no leftover v1/JAR signature files may remain — their presence (valid or
+# not) is what tripped Obtainium. Fail the build if any slipped through.
+if unzip -l "$APK_OUT" 2>/dev/null | grep -qiE 'META-INF/.*\.(SF|RSA|DSA|EC)$'; then
+  echo "ERROR: APK still contains v1/JAR signature files; expected v2+v3 only" >&2
+  exit 1
+fi
 
 echo ">>> done: $APK_OUT"