diff --git a/commons/src/main/java/commons/FormalIngredient.java b/commons/src/main/java/commons/FormalIngredient.java
index 32e5838..19f514c 100644
--- a/commons/src/main/java/commons/FormalIngredient.java
+++ b/commons/src/main/java/commons/FormalIngredient.java
@@ -52,14 +52,9 @@ public class FormalIngredient extends RecipeIngredient implements Scalable<Forma
         return amount + unitSuffix + " of " + ingredient.name;
     }
 
-    @Override
-    public FormalIngredient scaleBy(int numPortions) {
-        return new FormalIngredient(getIngredient(), amount * numPortions, unitSuffix);
-    }
-
     @Override
     public FormalIngredient scaleBy(double factor) {
-        return new FormalIngredient(getIngredient(), amount, unitSuffix);
+        return new FormalIngredient(getIngredient(), amount * factor, unitSuffix);
     }
 
     @Override
diff --git a/commons/src/main/java/commons/Scalable.java b/commons/src/main/java/commons/Scalable.java
index 7cb8a14..f2a3981 100644
--- a/commons/src/main/java/commons/Scalable.java
+++ b/commons/src/main/java/commons/Scalable.java
@@ -1,6 +1,8 @@
 package commons;
 
 public interface Scalable<IngredientType extends RecipeIngredient> {
-    IngredientType scaleBy(int numPortions);
+    default IngredientType scaleBy(int numPortions) {
+        return scaleBy((double) numPortions);
+    };
     IngredientType scaleBy(double factor);
 }