diff --git a/querydsl-core/src/main/java/com/querydsl/core/group/GAvg.java b/querydsl-core/src/main/java/com/querydsl/core/group/GAvg.java
index 5f289507e..bc96c837d 100644
--- a/querydsl-core/src/main/java/com/querydsl/core/group/GAvg.java
+++ b/querydsl-core/src/main/java/com/querydsl/core/group/GAvg.java
@@ -24,7 +24,7 @@ import com.querydsl.core.util.MathUtils;
  * @param <T>
  */
 @SuppressWarnings("unchecked")
-public class GAvg<T extends Number & Comparable<T>> extends AbstractGroupExpression<T, T> {
+public class GAvg<T extends Number> extends AbstractGroupExpression<T, T> {
 
     private static final long serialVersionUID = 3518868612387641383L;
 
diff --git a/querydsl-core/src/main/java/com/querydsl/core/group/GMax.java b/querydsl-core/src/main/java/com/querydsl/core/group/GMax.java
index d2805f07a..5ccbf13d3 100644
--- a/querydsl-core/src/main/java/com/querydsl/core/group/GMax.java
+++ b/querydsl-core/src/main/java/com/querydsl/core/group/GMax.java
@@ -20,7 +20,7 @@ import com.querydsl.core.types.Expression;
  *
  * @param <T>
  */
-class GMax<T extends Comparable<T>> extends AbstractGroupExpression<T, T> {
+class GMax<T extends Comparable<? super T>> extends AbstractGroupExpression<T, T> {
 
     private static final long serialVersionUID = 3815394663181131511L;
 
diff --git a/querydsl-core/src/main/java/com/querydsl/core/group/GMin.java b/querydsl-core/src/main/java/com/querydsl/core/group/GMin.java
index c4dc364e6..559448827 100644
--- a/querydsl-core/src/main/java/com/querydsl/core/group/GMin.java
+++ b/querydsl-core/src/main/java/com/querydsl/core/group/GMin.java
@@ -20,7 +20,7 @@ import com.querydsl.core.types.Expression;
  *
  * @param <T>
  */
-class GMin<T extends Comparable<T>> extends AbstractGroupExpression<T, T> {
+class GMin<T extends Comparable<? super T>> extends AbstractGroupExpression<T, T> {
 
     private static final long serialVersionUID = 8312168556148122576L;
 
diff --git a/querydsl-core/src/main/java/com/querydsl/core/group/GSum.java b/querydsl-core/src/main/java/com/querydsl/core/group/GSum.java
index 481a13c36..9c5b5fb59 100644
--- a/querydsl-core/src/main/java/com/querydsl/core/group/GSum.java
+++ b/querydsl-core/src/main/java/com/querydsl/core/group/GSum.java
@@ -24,7 +24,7 @@ import com.querydsl.core.util.MathUtils;
  * @param <T>
  */
 @SuppressWarnings("unchecked")
-public class GSum<T extends Number & Comparable<T>> extends AbstractGroupExpression<T, T> {
+public class GSum<T extends Number> extends AbstractGroupExpression<T, T> {
 
     private static final long serialVersionUID = 3518868612387641383L;
 
diff --git a/querydsl-core/src/main/java/com/querydsl/core/group/GroupBy.java b/querydsl-core/src/main/java/com/querydsl/core/group/GroupBy.java
index 32062297b..24b03893b 100644
--- a/querydsl-core/src/main/java/com/querydsl/core/group/GroupBy.java
+++ b/querydsl-core/src/main/java/com/querydsl/core/group/GroupBy.java
@@ -57,7 +57,7 @@ public final class GroupBy {
      * @param expression
      * @return
      */
-    public static <E extends Comparable<E>> AbstractGroupExpression<E, E> min(Expression<E> expression) {
+    public static <E extends Comparable<? super E>> AbstractGroupExpression<E, E> min(Expression<E> expression) {
         return new GMin<E>(expression);
     }
 
@@ -67,7 +67,7 @@ public final class GroupBy {
      * @param expression
      * @return
      */
-    public static <E extends Number & Comparable<E>> AbstractGroupExpression<E, E> sum(Expression<E> expression) {
+    public static <E extends Number> AbstractGroupExpression<E, E> sum(Expression<E> expression) {
         return new GSum<E>(expression);
     }
 
@@ -77,7 +77,7 @@ public final class GroupBy {
      * @param expression
      * @return
      */
-    public static <E extends Number & Comparable<E>> AbstractGroupExpression<E, E> avg(Expression<E> expression) {
+    public static <E extends Number> AbstractGroupExpression<E, E> avg(Expression<E> expression) {
         return new GAvg<E>(expression);
     }
 
@@ -87,7 +87,7 @@ public final class GroupBy {
      * @param expression
      * @return
      */
-    public static <E extends Comparable<E>> AbstractGroupExpression<E, E> max(Expression<E> expression) {
+    public static <E extends Comparable<? super E>> AbstractGroupExpression<E, E> max(Expression<E> expression) {
         return new GMax<E>(expression);
     }