diff --git a/BUILD b/BUILD
index 31e93b798b..6e7d35f55c 100644
--- a/BUILD
+++ b/BUILD
@@ -436,6 +436,47 @@ sh_test(
     deps = ["@bazel_tools//tools/bash/runfiles"],
 )
 
+cc_binary(
+    name = "conformance_upb_dynamic_minitable",
+    testonly = 1,
+    srcs = ["upb/conformance_upb.c"],
+    copts = UPB_DEFAULT_COPTS + [
+        "-DREBUILD_MINITABLES"
+    ],
+    data = ["upb/conformance_upb_failures.txt"],
+    deps = [
+        ":conformance_proto_upb",
+        ":conformance_proto_upbdefs",
+        ":test_messages_proto2_upbdefs",
+        ":test_messages_proto3_upbdefs",
+        "//:json",
+        "//:port",
+        "//:reflection",
+        "//:textformat",
+        "//:upb",
+    ],
+)
+
+make_shell_script(
+    name = "gen_test_conformance_upb_dynamic_minitable",
+    out = "test_conformance_upb_dynamic_minitable.sh",
+    contents = "external/com_google_protobuf/conformance_test_runner " +
+               " --enforce_recommended " +
+               " --failure_list ./upb/conformance_upb_failures.txt" +
+               " ./conformance_upb_dynamic_minitable",
+)
+
+sh_test(
+    name = "test_conformance_upb_dynamic_minitable",
+    srcs = ["test_conformance_upb_dynamic_minitable.sh"],
+    data = [
+        "upb/conformance_upb_failures.txt",
+        ":conformance_upb_dynamic_minitable",
+        "@com_google_protobuf//:conformance_test_runner",
+    ],
+    deps = ["@bazel_tools//tools/bash/runfiles"],
+)
+
 # Internal C/C++ libraries #####################################################
 
 cc_library(
diff --git a/upb/conformance_upb.c b/upb/conformance_upb.c
index 5f912f0c40..d696e961df 100644
--- a/upb/conformance_upb.c
+++ b/upb/conformance_upb.c
@@ -323,8 +323,13 @@ bool DoTestIo(upb_DefPool* symtab) {
 int main(void) {
   upb_DefPool* symtab = upb_DefPool_New();
 
+#ifdef REBUILD_MINITABLES
+  _upb_DefPool_LoadDefInitEx(symtab, &src_google_protobuf_test_messages_proto2_proto_upbdefinit, true);
+  _upb_DefPool_LoadDefInitEx(symtab, &src_google_protobuf_test_messages_proto3_proto_upbdefinit, true);
+#else
   protobuf_test_messages_proto2_TestAllTypesProto2_getmsgdef(symtab);
   protobuf_test_messages_proto3_TestAllTypesProto3_getmsgdef(symtab);
+#endif
 
   while (1) {
     if (!DoTestIo(symtab)) {
diff --git a/upb/def.c b/upb/def.c
index 712d68d638..4528030d0d 100644
--- a/upb/def.c
+++ b/upb/def.c
@@ -1413,7 +1413,11 @@ static uint8_t map_descriptortype(const upb_FieldDef* f) {
   if (type == kUpb_FieldType_String && f->file->syntax == kUpb_Syntax_Proto2) {
     return kUpb_FieldType_Bytes;
   } else if (type == kUpb_FieldType_Enum &&
-             f->sub.enumdef->file->syntax == kUpb_Syntax_Proto3) {
+             (f->sub.enumdef->file->syntax == kUpb_Syntax_Proto3 ||
+             // TODO(https://github.com/protocolbuffers/upb/issues/541):
+             // fix map enum values to check for unknown enum values and put
+             // them in the unknown field set.
+             upb_MessageDef_IsMapEntry(upb_FieldDef_ContainingType(f)))) {
     return kUpb_FieldType_Int32;
   }
   return type;