diff --git a/DMRCSBK.h b/DMRCSBK.h
index 9f24971..169023b 100644
--- a/DMRCSBK.h
+++ b/DMRCSBK.h
@@ -24,7 +24,7 @@
 
 #if defined(USE_DMR)
 
-enum class CSBKO {
+enum class CSBKO : unsigned char {
 	NONE           = 0x00,
 	UUVREQ         = 0x04,
 	UUANSRSP       = 0x05,
diff --git a/DMRDefines.h b/DMRDefines.h
index 639b737..7c2d47f 100644
--- a/DMRDefines.h
+++ b/DMRDefines.h
@@ -110,7 +110,7 @@ const unsigned char DPF_PROPRIETARY      = 0x0FU;
 const unsigned char FID_ETSI = 0U;
 const unsigned char FID_DMRA = 16U;
 
-enum class FLCO {
+enum class FLCO : unsigned char {
 	GROUP               = 0,
 	USER_USER           = 3,
 	TALKER_ALIAS_HEADER = 4,