diff --git a/Eigen/src/Core/ArithmeticSequence.h b/Eigen/src/Core/ArithmeticSequence.h
index 238601818..b425b7804 100644
--- a/Eigen/src/Core/ArithmeticSequence.h
+++ b/Eigen/src/Core/ArithmeticSequence.h
@@ -526,7 +526,7 @@ struct MakeIndexing<all_t> {
   typedef AllRange type;
 };
 
-AllRange make_indexing(all_t , Index size) {
+inline AllRange make_indexing(all_t , Index size) {
   return AllRange(size);
 }