diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7713dd2b..753e2437 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Fixed double comparison in SolutionCostPair.compareTo(SolutionCostPair).
 * Added missing equals and hashCode methods to SolutionCostPair.
 * Fixed end of line characters when writing weighted static scheduling instances to file.
+* WeightedStaticScheduling: fixed constants that should be static fields.
 
 ### Dependencies
 
diff --git a/src/main/java/org/cicirello/search/problems/scheduling/WeightedStaticScheduling.java b/src/main/java/org/cicirello/search/problems/scheduling/WeightedStaticScheduling.java
index 80bcdd06..11560fb5 100644
--- a/src/main/java/org/cicirello/search/problems/scheduling/WeightedStaticScheduling.java
+++ b/src/main/java/org/cicirello/search/problems/scheduling/WeightedStaticScheduling.java
@@ -93,8 +93,8 @@ public final class WeightedStaticScheduling implements SingleMachineSchedulingPr
   private final int[] duedates;
   private final int[] weights;
 
-  private final int PROCESS_TIME_SPAN = MAX_PROCESS_TIME - MIN_PROCESS_TIME + 1;
-  private final int WEIGHT_SPAN = MAX_WEIGHT - MIN_WEIGHT + 1;
+  private static final int PROCESS_TIME_SPAN = MAX_PROCESS_TIME - MIN_PROCESS_TIME + 1;
+  private static final int WEIGHT_SPAN = MAX_WEIGHT - MIN_WEIGHT + 1;
 
   /**
    * Generates random single machine scheduling problem instances.