diff --git a/input.c b/input.c
index 5e7d3420..7c1004f9 100644
--- a/input.c
+++ b/input.c
@@ -884,6 +884,21 @@ keymap_lookup(struct terminal *term, xkb_keysym_t sym, enum modifier mods)
     return NULL;
 }
 
+#if defined(_DEBUG)
+static void __attribute__((constructor))
+test_keymap_lookup(void)
+{
+    struct terminal term = {
+        .num_lock_modifier = false,
+        .keypad_keys_mode = KEYPAD_NUMERICAL,
+        .cursor_keys_mode = CURSOR_KEYS_NORMAL,
+    };
+
+    const struct key_data *info = keymap_lookup(&term, XKB_KEY_ISO_Left_Tab, MOD_SHIFT | MOD_CTRL);
+    xassert(strcmp(info->seq, "\033[27;6;9~") == 0);
+}
+#endif
+
 static void
 key_press_release(struct seat *seat, struct terminal *term, uint32_t serial,
                   uint32_t key, uint32_t state)