diff --git a/src/settings_type.h b/src/settings_type.h
index c873beb30a..2b7a930f14 100644
--- a/src/settings_type.h
+++ b/src/settings_type.h
@@ -65,14 +65,14 @@ enum IndustryDensity {
 };
 
 /** Possible values for "use_relay_service" setting. */
-enum UseRelayService {
+enum UseRelayService : uint8_t {
 	URS_NEVER = 0,
 	URS_ASK,
 	URS_ALLOW,
 };
 
 /** Possible values for "participate_survey" setting. */
-enum ParticipateSurvey {
+enum ParticipateSurvey : uint8_t {
 	PS_ASK = 0,
 	PS_NO,
 	PS_YES,
diff --git a/src/signal_type.h b/src/signal_type.h
index 042f0b9fea..10097c7c22 100644
--- a/src/signal_type.h
+++ b/src/signal_type.h
@@ -23,7 +23,7 @@ enum SignalVariant {
 
 
 /** Type of signal, i.e. how does the signal behave? */
-enum SignalType {
+enum SignalType : uint8 {
 	SIGTYPE_NORMAL     = 0, ///< normal signal
 	SIGTYPE_ENTRY      = 1, ///< presignal block entry
 	SIGTYPE_EXIT       = 2, ///< presignal block exit
diff --git a/src/zoning.h b/src/zoning.h
index c24daefbd6..3401b3548a 100644
--- a/src/zoning.h
+++ b/src/zoning.h
@@ -16,7 +16,7 @@
 /**
  * Zoning evaluation modes
  */
-enum ZoningEvaluationMode {
+enum ZoningEvaluationMode : uint8 {
 	ZEM_NOTHING = 0,   ///< No zoning action selected
 	ZEM_AUTHORITY,     ///< Check the local authority's opinion.
 	ZEM_CAN_BUILD,     ///< Check wither or not the player can build.