diff --git a/app/src/main/java/org/isoron/uhabits/helpers/UIHelper.java b/app/src/main/java/org/isoron/uhabits/helpers/UIHelper.java
index 3a2a8c7bd..a5983e8b5 100644
--- a/app/src/main/java/org/isoron/uhabits/helpers/UIHelper.java
+++ b/app/src/main/java/org/isoron/uhabits/helpers/UIHelper.java
@@ -23,6 +23,7 @@ import android.content.Context;
 import android.content.SharedPreferences;
 import android.content.res.Resources;
 import android.graphics.Typeface;
+import android.os.Looper;
 import android.preference.PreferenceManager;
 import android.util.AttributeSet;
 import android.util.DisplayMetrics;
@@ -110,4 +111,19 @@ public abstract class UIHelper
         DisplayMetrics metrics = resources.getDisplayMetrics();
         return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, sp, metrics);
     }
+
+    /**
+     * Throws a runtime exception if called from the main thread. Useful to make sure that
+     * slow methods never accidentally slow the application down.
+     *
+     * @throws RuntimeException when run from main thread
+     */
+    public static void throwIfMainThread() throws RuntimeException
+    {
+        Looper looper = Looper.myLooper();
+        if(looper == null) return;
+
+        if(looper == Looper.getMainLooper())
+            throw new RuntimeException("This method should never be called from the main thread");
+    }
 }
diff --git a/app/src/main/java/org/isoron/uhabits/models/CheckmarkList.java b/app/src/main/java/org/isoron/uhabits/models/CheckmarkList.java
index f761f26c9..865e4c358 100644
--- a/app/src/main/java/org/isoron/uhabits/models/CheckmarkList.java
+++ b/app/src/main/java/org/isoron/uhabits/models/CheckmarkList.java
@@ -30,6 +30,7 @@ import com.activeandroid.query.Delete;
 import com.activeandroid.query.Select;
 
 import org.isoron.uhabits.helpers.DateHelper;
+import org.isoron.uhabits.helpers.UIHelper;
 
 import java.io.IOException;
 import java.io.Writer;
@@ -151,6 +152,8 @@ public class CheckmarkList
      */
     protected void compute(long from, final long to)
     {
+        UIHelper.throwIfMainThread();
+
         final long day = DateHelper.millisecondsInOneDay;
 
         Checkmark newestCheckmark = findNewest();
diff --git a/app/src/main/java/org/isoron/uhabits/models/ScoreList.java b/app/src/main/java/org/isoron/uhabits/models/ScoreList.java
index 9146ed3c8..06331885d 100644
--- a/app/src/main/java/org/isoron/uhabits/models/ScoreList.java
+++ b/app/src/main/java/org/isoron/uhabits/models/ScoreList.java
@@ -33,6 +33,7 @@ import com.activeandroid.util.SQLiteUtils;
 
 import org.isoron.uhabits.helpers.DatabaseHelper;
 import org.isoron.uhabits.helpers.DateHelper;
+import org.isoron.uhabits.helpers.UIHelper;
 
 import java.io.IOException;
 import java.io.Writer;
@@ -102,6 +103,8 @@ public class ScoreList
      */
     protected void compute(long from, long to)
     {
+        UIHelper.throwIfMainThread();
+
         final long day = DateHelper.millisecondsInOneDay;
         final double freq = ((double) habit.freqNum) / habit.freqDen;
 
diff --git a/app/src/main/java/org/isoron/uhabits/models/StreakList.java b/app/src/main/java/org/isoron/uhabits/models/StreakList.java
index f8a296ae2..691403d25 100644
--- a/app/src/main/java/org/isoron/uhabits/models/StreakList.java
+++ b/app/src/main/java/org/isoron/uhabits/models/StreakList.java
@@ -28,6 +28,7 @@ import com.activeandroid.query.Delete;
 import com.activeandroid.query.Select;
 
 import org.isoron.uhabits.helpers.DateHelper;
+import org.isoron.uhabits.helpers.UIHelper;
 
 import java.util.ArrayList;
 import java.util.LinkedList;
@@ -86,6 +87,8 @@ public class StreakList
 
     public void rebuild()
     {
+        UIHelper.throwIfMainThread();
+
         long beginning;
         long today = DateHelper.getStartOfToday();
         long day = DateHelper.millisecondsInOneDay;