diff --git a/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs b/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs
index 1c4259e4..781ad4a6 100644
--- a/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs
+++ b/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs
@@ -189,8 +189,12 @@ public RDFPatternGroup AddPropertyPath(RDFPropertyPath propertyPath)
         public RDFPatternGroup AddValues(RDFValues values)
         {
             if (values != null)
-                this.GroupMembers.Add(values);
-
+            {
+                if (!this.GetValues().Any(v => v.Equals(values)))
+                {
+                    this.GroupMembers.Add(values);
+                }
+            }
             return this;
         }
 
@@ -268,7 +272,7 @@ internal RDFPatternGroup AddInjectedValues(RDFValues values)
                 clonedValues.IsEvaluable = values.IsEvaluable;
                 clonedValues.IsInjected = true;
 
-                this.GroupMembers.Add(clonedValues);
+                this.AddValues(clonedValues);
             }
             return this;
         }
diff --git a/RDFSharp/Query/Mirella/RDFQueryEngine.cs b/RDFSharp/Query/Mirella/RDFQueryEngine.cs
index 727547be..72ecb715 100644
--- a/RDFSharp/Query/Mirella/RDFQueryEngine.cs
+++ b/RDFSharp/Query/Mirella/RDFQueryEngine.cs
@@ -605,7 +605,9 @@ internal void EvaluatePatternGroup(RDFQuery query, RDFPatternGroup patternGroup,
             QueryMemberTemporaryResultTables[patternGroup.QueryMemberID] = new List<DataTable>();
 
             //Iterate the evaluable members of the pattern group
-            List<RDFPatternGroupMember> evaluablePGMembers = patternGroup.GetEvaluablePatternGroupMembers().ToList();
+            List<RDFPatternGroupMember> evaluablePGMembers = patternGroup.GetEvaluablePatternGroupMembers()
+                                                                         .Distinct()
+                                                                         .ToList();
             foreach (RDFPatternGroupMember evaluablePGMember in evaluablePGMembers)
             {