diff --git a/src/coins.h b/src/coins.h
index dca1beabb..d8135e0d9 100644
--- a/src/coins.h
+++ b/src/coins.h
@@ -95,8 +95,16 @@ public:
      * This *must* return size_t. With Boost 1.46 on 32-bit systems the
      * unordered_map will behave unpredictably if the custom hasher returns a
      * uint64_t, resulting in failures when syncing the chain (#4634).
+     *
+     * Having the hash noexcept allows libstdc++'s unordered_map to recalculate
+     * the hash during rehash, so it does not have to cache the value. This
+     * reduces node's memory by sizeof(size_t). The required recalculation has
+     * a slight performance penalty (around 1.6%), but this is compensated by
+     * memory savings of about 9% which allow for a larger dbcache setting.
+     *
+     * @see https://gcc.gnu.org/onlinedocs/gcc-9.2.0/libstdc++/manual/manual/unordered_associative.html
      */
-    size_t operator()(const COutPoint& id) const {
+    size_t operator()(const COutPoint& id) const noexcept {
         return SipHashUint256Extra(k0, k1, id.hash, id.n);
     }
 };