diff --git a/src/wallet/init.cpp b/src/wallet/init.cpp
--- a/src/wallet/init.cpp
+++ b/src/wallet/init.cpp
@@ -57,10 +57,14 @@
                            "disable the fallbackfee feature. (default: %s)",
                            CURRENCY_UNIT, FormatMoney(DEFAULT_FALLBACK_FEE)),
                  ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
-    gArgs.AddArg("-keypool=<n>",
-                 strprintf("Set key pool size to <n> (default: %u)",
-                           DEFAULT_KEYPOOL_SIZE),
-                 ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
+    gArgs.AddArg(
+        "-keypool=<n>",
+        strprintf("Set key pool size to <n> (default: %u). Warning: Smaller "
+                  "sizes may increase the risk of losing funds when restoring "
+                  "from an old backup, if none of the addresses in the "
+                  "original keypool have been used.",
+                  DEFAULT_KEYPOOL_SIZE),
+        ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
     gArgs.AddArg(
         "-maxapsfee=<n>",
         strprintf(
diff --git a/src/wallet/scriptpubkeyman.h b/src/wallet/scriptpubkeyman.h
--- a/src/wallet/scriptpubkeyman.h
+++ b/src/wallet/scriptpubkeyman.h
@@ -79,6 +79,11 @@
  * keys (by default 1000) ahead of the last used key and scans for the
  * addresses of those keys.  This avoids the risk of not seeing transactions
  * involving the wallet's addresses, or of re-using the same address.
+ * In the unlikely case where none of the addresses in the `gap limit` are
+ * used on-chain, the look-ahead will not be incremented to keep
+ * a constant size and addresses beyond this range will not be detected by an
+ * old backup. For this reason, it is not recommended to decrease keypool size
+ * lower than default value.
  *
  * The HD-split wallet feature added a second keypool (commit: 02592f4c). There
  * is an external keypool (for addresses to hand out) and an internal keypool