diff --git a/headers/os/support/StringList.h b/headers/os/support/StringList.h
index efd3546404..c1938121f2 100644
--- a/headers/os/support/StringList.h
+++ b/headers/os/support/StringList.h
@@ -53,7 +53,8 @@ public:
 			int32				CountStrings() const;
 			bool				IsEmpty() const;
 
-			BString				Join(const char* separator, int32 length = -1);
+			BString				Join(const char* separator, int32 length = -1)
+									const;
 
 	// Iteration
 			void				DoForEach(bool (*func)(const BString& string));
@@ -77,7 +78,8 @@ private:
 			void				_IncrementRefCounts() const;
 			void				_DecrementRefCounts() const;
 
-			BString				_Join(const char* separator, int32 length);
+			BString				_Join(const char* separator, int32 length)
+									const;
 
 private:
 			BList				fStrings;
diff --git a/src/kits/support/StringList.cpp b/src/kits/support/StringList.cpp
index 20dc9ccd4c..8d51f3f0af 100644
--- a/src/kits/support/StringList.cpp
+++ b/src/kits/support/StringList.cpp
@@ -276,7 +276,7 @@ BStringList::IsEmpty() const
 
 
 BString
-BStringList::Join(const char* separator, int32 length)
+BStringList::Join(const char* separator, int32 length) const
 {
 	return _Join(separator,
 		length >= 0 ? strnlen(separator, length) : strlen(separator));
@@ -434,7 +434,7 @@ BStringList::_DecrementRefCounts() const
 
 
 BString
-BStringList::_Join(const char* separator, int32 length)
+BStringList::_Join(const char* separator, int32 length) const
 {
 	// handle simple cases (0 or 1 element)
 	int32 count = CountStrings();