diff --git a/lardataalg/Utilities/MultipleChoiceSelection.h b/lardataalg/Utilities/MultipleChoiceSelection.h
index dc172a72..8406e443 100644
--- a/lardataalg/Utilities/MultipleChoiceSelection.h
+++ b/lardataalg/Utilities/MultipleChoiceSelection.h
@@ -491,25 +491,26 @@ bool my_lexicographical_compare(B1 b1, E1 e1, B2 b2, E2 e2, Comp less)
   return true; // 1 is shorter
 } // my_lexicographical_compare()
 
-bool util::details::CaseInsensitiveComparer::equal(std::string const& a, std::string const& b)
+inline bool util::details::CaseInsensitiveComparer::equal(std::string const& a,
+                                                          std::string const& b)
 {
   return std::equal(a.begin(), a.end(), b.begin(), b.end(), eq_lower);
 }
 
 // -----------------------------------------------------------------------------
-bool util::details::CaseInsensitiveComparer::less(std::string const& a, std::string const& b)
+inline bool util::details::CaseInsensitiveComparer::less(std::string const& a, std::string const& b)
 {
   return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end(), cmp_lower);
 } // util::details::CaseInsensitiveComparer::less()
 
 // -----------------------------------------------------------------------------
-bool util::details::CaseInsensitiveComparer::cmp_lower(unsigned char a, unsigned char b)
+inline bool util::details::CaseInsensitiveComparer::cmp_lower(unsigned char a, unsigned char b)
 {
   return std::tolower(a) < std::tolower(b);
 }
 
 // -----------------------------------------------------------------------------
-bool util::details::CaseInsensitiveComparer::eq_lower(unsigned char a, unsigned char b)
+inline bool util::details::CaseInsensitiveComparer::eq_lower(unsigned char a, unsigned char b)
 {
   return std::tolower(a) == std::tolower(b);
 }