diff --git a/src/kits/support/CharacterSetRoster.cpp b/src/kits/support/CharacterSetRoster.cpp
index eb7a0db6ea..7ce1475cf5 100644
--- a/src/kits/support/CharacterSetRoster.cpp
+++ b/src/kits/support/CharacterSetRoster.cpp
@@ -54,18 +54,27 @@ BCharacterSetRoster::StopWatching(BMessenger target)
 const BCharacterSet * 
 BCharacterSetRoster::GetCharacterSetByFontID(uint32 id)
 {
+	if ((id < 0) || (id >= character_sets_by_id_count)) {
+		return NULL;
+	}
 	return character_sets_by_id[id];
 }
 
 const BCharacterSet * 
 BCharacterSetRoster::GetCharacterSetByConversionID(uint32 id)
 {
+	if ((id+1 < 0) || (id+1 >= character_sets_by_id_count)) {
+		return NULL;
+	}
 	return character_sets_by_id[id+1];
 }
 
 const BCharacterSet * 
 BCharacterSetRoster::GetCharacterSetByMIBenum(uint32 MIBenum)
 {
+	if ((MIBenum < 0) || (MIBenum > maximum_valid_MIBenum)) {
+		return NULL;
+	}
 	return character_sets_by_MIBenum[MIBenum];
 }