diff --git a/.clang-tidy b/.clang-tidy
index 314521eece..215b5a5e26 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -1,6 +1,7 @@
 Checks: [-*,
          bugprone-*,
          performance-avoid-endl,
+         performance-enum-size,
 
          # Skipping these temporarily because they are very noisy
          -bugprone-narrowing-conversions,
diff --git a/src/analyzer/protocol/http/HTTP.cc b/src/analyzer/protocol/http/HTTP.cc
index 4aefbea232..7a72b9fd12 100644
--- a/src/analyzer/protocol/http/HTTP.cc
+++ b/src/analyzer/protocol/http/HTTP.cc
@@ -20,14 +20,14 @@ const bool DEBUG_http = false;
 
 // The EXPECT_*_NOTHING states are used to prevent further parsing. Used if a
 // message was interrupted.
-enum HTTP_ExpectRequest {
+enum HTTP_ExpectRequest : uint8_t {
     EXPECT_REQUEST_LINE,
     EXPECT_REQUEST_MESSAGE,
     EXPECT_REQUEST_TRAILER,
     EXPECT_REQUEST_NOTHING,
 };
 
-enum HTTP_ExpectReply {
+enum HTTP_ExpectReply : uint8_t {
     EXPECT_REPLY_LINE,
     EXPECT_REPLY_MESSAGE,
     EXPECT_REPLY_TRAILER,
diff --git a/src/analyzer/protocol/mime/MIME.cc b/src/analyzer/protocol/mime/MIME.cc
index 5965f70242..e306bc874f 100644
--- a/src/analyzer/protocol/mime/MIME.cc
+++ b/src/analyzer/protocol/mime/MIME.cc
@@ -30,13 +30,13 @@ int mime_header_only = 0;
 int mime_decode_data = 1;
 int mime_submit_data = 1;
 
-enum MIME_HEADER_FIELDS {
+enum MIME_HEADER_FIELDS : uint8_t {
     MIME_CONTENT_TYPE,
     MIME_CONTENT_TRANSFER_ENCODING,
     MIME_FIELD_OTHER,
 };
 
-enum MIME_CONTENT_SUBTYPE {
+enum MIME_CONTENT_SUBTYPE : uint8_t {
     CONTENT_SUBTYPE_MIXED,       // for multipart
     CONTENT_SUBTYPE_ALTERNATIVE, // for multipart
     CONTENT_SUBTYPE_DIGEST,      // for multipart
@@ -50,7 +50,7 @@ enum MIME_CONTENT_SUBTYPE {
     CONTENT_SUBTYPE_OTHER,
 };
 
-enum MIME_CONTENT_ENCODING {
+enum MIME_CONTENT_ENCODING : uint8_t {
     CONTENT_ENCODING_7BIT,
     CONTENT_ENCODING_8BIT,
     CONTENT_ENCODING_BINARY,
@@ -59,7 +59,7 @@ enum MIME_CONTENT_ENCODING {
     CONTENT_ENCODING_OTHER,
 };
 
-enum MIME_BOUNDARY_DELIMITER {
+enum MIME_BOUNDARY_DELIMITER : uint8_t {
     NOT_MULTIPART_BOUNDARY,
     MULTIPART_BOUNDARY,
     MULTIPART_CLOSING_BOUNDARY,
diff --git a/src/cluster/backend/zeromq/ZeroMQ.cc b/src/cluster/backend/zeromq/ZeroMQ.cc
index 077100c000..0479a8bf06 100644
--- a/src/cluster/backend/zeromq/ZeroMQ.cc
+++ b/src/cluster/backend/zeromq/ZeroMQ.cc
@@ -39,7 +39,7 @@ extern zeek::plugin::Zeek_Cluster_Backend_ZeroMQ::Plugin plugin;
 
 namespace cluster::zeromq {
 
-enum class DebugFlag : zeek_uint_t {
+enum class DebugFlag : uint8_t {
     NONE = 0,
     POLL = 1,
     THREAD = 2,
@@ -50,9 +50,7 @@ enum class InprocTag : uint8_t {
     Terminate,
 };
 
-constexpr DebugFlag operator&(zeek_uint_t x, DebugFlag y) {
-    return static_cast<DebugFlag>(x & static_cast<zeek_uint_t>(y));
-}
+constexpr DebugFlag operator&(uint8_t x, DebugFlag y) { return static_cast<DebugFlag>(x & static_cast<uint8_t>(y)); }
 
 #define ZEROMQ_DEBUG(...) PLUGIN_DBG_LOG(zeek::plugin::Zeek_Cluster_Backend_ZeroMQ::plugin, __VA_ARGS__)
 
diff --git a/src/input/ReaderBackend.cc b/src/input/ReaderBackend.cc
index 664ffb10ab..4031c74f8b 100644
--- a/src/input/ReaderBackend.cc
+++ b/src/input/ReaderBackend.cc
@@ -49,7 +49,7 @@ private:
 
 class ReaderErrorMessage final : public threading::OutputMessage<ReaderFrontend> {
 public:
-    enum Type { INFO, WARNING, ERROR };
+    enum Type : uint8_t { INFO, WARNING, ERROR };
 
     ReaderErrorMessage(ReaderFrontend* reader, Type arg_type, const char* arg_msg)
         : threading::OutputMessage<ReaderFrontend>("ReaderErrorMessage", reader) {
diff --git a/src/packet_analysis/protocol/icmp/ICMP.cc b/src/packet_analysis/protocol/icmp/ICMP.cc
index d53361652b..5c40363acd 100644
--- a/src/packet_analysis/protocol/icmp/ICMP.cc
+++ b/src/packet_analysis/protocol/icmp/ICMP.cc
@@ -15,11 +15,6 @@
 #include "zeek/packet_analysis/protocol/icmp/events.bif.h"
 #include "zeek/session/Manager.h"
 
-enum ICMP_EndpointState {
-    ICMP_INACTIVE, // no packet seen
-    ICMP_ACTIVE,   // packets seen
-};
-
 using namespace zeek::packet_analysis::ICMP;
 using namespace zeek::packet_analysis::IP;
 
diff --git a/src/packet_analysis/protocol/icmp/ICMPSessionAdapter.cc b/src/packet_analysis/protocol/icmp/ICMPSessionAdapter.cc
index 3dbefd9c62..472df6a098 100644
--- a/src/packet_analysis/protocol/icmp/ICMPSessionAdapter.cc
+++ b/src/packet_analysis/protocol/icmp/ICMPSessionAdapter.cc
@@ -9,7 +9,7 @@
 using namespace zeek::packet_analysis::ICMP;
 using namespace zeek::packet_analysis::IP;
 
-enum ICMP_EndpointState {
+enum ICMP_EndpointState : uint8_t {
     ICMP_INACTIVE, // no packet seen
     ICMP_ACTIVE,   // packets seen
 };
diff --git a/src/packet_analysis/protocol/udp/UDPSessionAdapter.cc b/src/packet_analysis/protocol/udp/UDPSessionAdapter.cc
index 932a06f2dc..8f0a1761d8 100644
--- a/src/packet_analysis/protocol/udp/UDPSessionAdapter.cc
+++ b/src/packet_analysis/protocol/udp/UDPSessionAdapter.cc
@@ -9,7 +9,7 @@
 using namespace zeek::packet_analysis::UDP;
 using namespace zeek::packet_analysis::IP;
 
-enum UDP_EndpointState {
+enum UDP_EndpointState : uint8_t {
     UDP_INACTIVE, // no packet seen
     UDP_ACTIVE,   // packets seen
 };
diff --git a/src/threading/MsgThread.cc b/src/threading/MsgThread.cc
index 81764bbda8..144737ff4d 100644
--- a/src/threading/MsgThread.cc
+++ b/src/threading/MsgThread.cc
@@ -69,7 +69,7 @@ private:
 // A message from the child to be passed on to the Reporter.
 class ReporterMessage final : public OutputMessage<MsgThread> {
 public:
-    enum Type { INFO, WARNING, ERROR, FATAL_ERROR, FATAL_ERROR_WITH_CORE, INTERNAL_WARNING, INTERNAL_ERROR };
+    enum Type : uint8_t { INFO, WARNING, ERROR, FATAL_ERROR, FATAL_ERROR_WITH_CORE, INTERNAL_WARNING, INTERNAL_ERROR };
 
     ReporterMessage(Type arg_type, MsgThread* thread, std::string_view arg_msg)
         : OutputMessage<MsgThread>("ReporterMessage", thread) {