diff --git a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ActivationRuleGroup.java b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ActivationRuleGroup.java
index ba7369d..7c72830 100644
--- a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ActivationRuleGroup.java
+++ b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ActivationRuleGroup.java
@@ -33,6 +33,8 @@ import java.util.TreeSet;
  * rule and ignores other rules in the group (XOR logic).
  * Rules are first sorted by their natural order (priority by default) within the group.
  *
+ * <strong>This class is not thread-safe.</strong>
+ * 
  * @author Mahmoud Ben Hassine (mahmoud.benhassine@icloud.com)
  */
 public class ActivationRuleGroup extends CompositeRule {
diff --git a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/CompositeRule.java b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/CompositeRule.java
index 70a6633..b6d506b 100644
--- a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/CompositeRule.java
+++ b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/CompositeRule.java
@@ -35,6 +35,9 @@ import java.util.TreeSet;
 
 /**
  * Base class representing a composite rule composed of a set of rules.
+ * 
+ * <strong>This class is not thread-safe.
+ * Sub-classes are inherently not thread-safe.</strong>
  *
  * @author Mahmoud Ben Hassine (mahmoud.benhassine@icloud.com)
  */
diff --git a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ConditionalRuleGroup.java b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ConditionalRuleGroup.java
index 3167c0c..aa797ca 100644
--- a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ConditionalRuleGroup.java
+++ b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/ConditionalRuleGroup.java
@@ -37,6 +37,8 @@ import java.util.Set;
  * priority acts as a condition: if the rule with the highest priority evaluates
  * to true, then we try to evaluate the rest of the rules and execute the ones
  * that evaluate to true.
+ * 
+ * <strong>This class is not thread-safe.</strong>
  *
  * @author Dag Framstad (dagframstad@gmail.com)
  */
diff --git a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/UnitRuleGroup.java b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/UnitRuleGroup.java
index af5b2d6..3c794cc 100644
--- a/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/UnitRuleGroup.java
+++ b/easy-rules-support/src/main/java/org/jeasy/rules/support/composite/UnitRuleGroup.java
@@ -29,6 +29,8 @@ import org.jeasy.rules.api.Rule;
 /**
  * A unit rule group is a composite rule that acts as a unit: Either all rules are
  * applied or nothing is applied (all or nothing semantic).
+ * 
+ * <strong>This class is not thread-safe.</strong>
  *
  *  @author Mahmoud Ben Hassine (mahmoud.benhassine@icloud.com)
  */