diff --git a/app/build.gradle b/app/build.gradle
index f901441..1b2a897 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -1,4 +1,4 @@
-apply plugin: 'android'
+apply plugin: 'com.android.application'
 android {
 	compileSdkVersion 19
 	buildToolsVersion '19.1.0'
diff --git a/app/src/main/java/com/nutomic/zertman/MovedCertificatesStorage.java b/app/src/main/java/com/nutomic/zertman/MovedCertificatesStorage.java
index 5e381f1..8b68b85 100644
--- a/app/src/main/java/com/nutomic/zertman/MovedCertificatesStorage.java
+++ b/app/src/main/java/com/nutomic/zertman/MovedCertificatesStorage.java
@@ -33,7 +33,9 @@ public class MovedCertificatesStorage implements Closeable {
 	}
 
 	public boolean insert(Certificate cert) {
-		assert(cert.isSystemCertificate());
+		if (BuildConfig.DEBUG && !cert.isSystemCertificate()) {
+			throw new InvalidParameterException("Only system certificates can be inserted");
+		}
 
 		ContentValues cv = new ContentValues();
 		cv.put(Table.COLUMN_NAME_FILE_NAME, cert.getFile().getName());
diff --git a/app/src/main/res/values-w820dp/dimens.xml b/app/src/main/res/values-w820dp/dimens.xml
deleted file mode 100644
index 63fc816..0000000
--- a/app/src/main/res/values-w820dp/dimens.xml
+++ /dev/null
@@ -1,6 +0,0 @@
-<resources>
-    <!-- Example customization of dimensions originally defined in res/values/dimens.xml
-         (such as screen margins) for screens with more than 820dp of available width. This
-         would include 7" and 10" devices in landscape (~960dp and ~1280dp respectively). -->
-    <dimen name="activity_horizontal_margin">64dp</dimen>
-</resources>
diff --git a/app/src/main/res/values/dimens.xml b/app/src/main/res/values/dimens.xml
deleted file mode 100644
index 47c8224..0000000
--- a/app/src/main/res/values/dimens.xml
+++ /dev/null
@@ -1,5 +0,0 @@
-<resources>
-    <!-- Default screen margins, per the Android Design guidelines. -->
-    <dimen name="activity_horizontal_margin">16dp</dimen>
-    <dimen name="activity_vertical_margin">16dp</dimen>
-</resources>