diff --git a/Eigen/src/Core/util/Constants.h b/Eigen/src/Core/util/Constants.h
index 1deb22340..4457f4f69 100644
--- a/Eigen/src/Core/util/Constants.h
+++ b/Eigen/src/Core/util/Constants.h
@@ -551,7 +551,7 @@ struct IteratorBased {};
 /** \internal
  * Constants for comparison functors
  */
-enum ComparisonName {
+enum ComparisonName : unsigned int {
   cmp_EQ = 0,
   cmp_LT = 1,
   cmp_LE = 2,