diff --git a/src/hb-cache.hh b/src/hb-cache.hh
index e617b75de..d6b229ed6 100644
--- a/src/hb-cache.hh
+++ b/src/hb-cache.hh
@@ -32,7 +32,7 @@
 
 /* Implements a lockfree cache for int->int functions. */
 
-template <unsigned int key_bits, unsigned int value_bits, unsigned int cache_bits>
+template <unsigned int key_bits=16, unsigned int value_bits=8 + 32 - key_bits, unsigned int cache_bits=8>
 struct hb_cache_t
 {
   static_assert ((key_bits >= cache_bits), "");