diff --git a/src/xcb_errors.c b/src/xcb_errors.c
index 428e7be..2eedc34 100644
--- a/src/xcb_errors.c
+++ b/src/xcb_errors.c
@@ -200,7 +200,8 @@ const char *xcb_errors_get_name_for_core_event(xcb_errors_context_t *ctx,
 		best = current;
 	}
 
-	if (best == NULL || best->first_event == 0) {
+	if (best == NULL || best->first_event == 0
+			|| event_code - best->first_event >= best->static_info->num_events) {
 		/* Nothing found */
 		return get_strings_entry(xproto_info.strings_events, event_code);
 	}
@@ -237,7 +238,8 @@ const char *xcb_errors_get_name_for_error(xcb_errors_context_t *ctx,
 		best = current;
 	}
 
-	if (best == NULL || best->first_error == 0) {
+	if (best == NULL || best->first_error == 0
+			|| error_code - best->first_error >= best->static_info->num_errors) {
 		/* Nothing found */
 		return get_strings_entry(xproto_info.strings_errors, error_code);
 	}
diff --git a/tests/test.c b/tests/test.c
index 67c01d0..bb7ba75 100644
--- a/tests/test.c
+++ b/tests/test.c
@@ -347,11 +347,13 @@ static int test_valid_connection(void)
 	err |= check_error(ctx, XCB_IMPLEMENTATION, "Implementation", NULL);
 	err |= check_error(ctx, 18, "Unknown (18)", NULL);
 	err |= check_error(ctx, 127, "Unknown (127)", NULL);
+	err |= check_error(ctx, 0xff, "Unknown (255)", NULL);
 
 	err |= check_event(ctx, XCB_KEY_PRESS, "KeyPress", NULL);
 	err |= check_event(ctx, XCB_KEY_RELEASE, "KeyRelease", NULL);
 	err |= check_event(ctx, XCB_GE_GENERIC, "GeGeneric", NULL);
 	err |= check_event(ctx, 36, "Unknown (36)", NULL);
+	err |= check_event(ctx, 127, "Unknown (127)", NULL);
 
 	err |= test_randr(c, ctx);
 	err |= test_xinput(c, ctx);