test: wallet: Constructing a DSPKM that can't TopUp() throws.

diff --git a/src/wallet/scriptpubkeyman.h b/src/wallet/scriptpubkeyman.h
index 621630c9..8b80a3da 100644
--- a/src/wallet/scriptpubkeyman.h
+++ b/src/wallet/scriptpubkeyman.h
@@ -168,14 +168,12 @@ static const std::unordered_set<OutputType> LEGACY_OUTPUT_TYPES {
 
 using KeyMap = std::map<CKeyID, CKey>;
 using CryptedKeyMap = std::map<CKeyID, std::pair<CPubKey, std::vector<unsigned char>>>;
-using ScriptPubKeyMap = std::map<CScript, int32_t>; // Map of scripts to descriptor range index
-using PubKeyMap = std::map<CPubKey, int32_t>; // Map of pubkeys involved in scripts to descriptor range index
 
 // Manages the data for a LegacyScriptPubKeyMan.
 // This is the minimum necessary to load a legacy wallet so that it can be migrated.
 class LegacyDataSPKM : public ScriptPubKeyMan, public FillableSigningProvider
 {
-protected:
+private:
     using WatchOnlySet = std::set<CScript>;
     using WatchKeyMap = std::map<CKeyID, CPubKey>;
 
@@ -277,6 +275,9 @@ class DescriptorScriptPubKeyMan : public ScriptPubKeyMan
 {
     friend class LegacyDataSPKM;
 private:
+    using ScriptPubKeyMap = std::map<CScript, int32_t>; // Map of scripts to descriptor range index
+    using PubKeyMap = std::map<CPubKey, int32_t>; // Map of pubkeys involved in scripts to descriptor range index
+
     ScriptPubKeyMap m_map_script_pub_keys GUARDED_BY(cs_desc_man);
     PubKeyMap m_map_pubkeys GUARDED_BY(cs_desc_man);
     int32_t m_max_cached_index = -1;
diff --git a/src/wallet/test/scriptpubkeyman_tests.cpp b/src/wallet/test/scriptpubkeyman_tests.cpp
index 9c62436d..74389a54 100644
--- a/src/wallet/test/scriptpubkeyman_tests.cpp
+++ b/src/wallet/test/scriptpubkeyman_tests.cpp
@@ -4,6 +4,7 @@
 
 #include <key.h>
 #include <key_io.h>
+#include <test/util/common.h>
 #include <test/util/setup_common.h>
 #include <script/solver.h>
 #include <wallet/scriptpubkeyman.h>
@@ -37,5 +38,17 @@ BOOST_AUTO_TEST_CASE(DescriptorScriptPubKeyManTests)
     BOOST_CHECK(signprov_keypath_nums_h == nullptr);
 }
 
+BOOST_AUTO_TEST_CASE(desc_spkm_topup_fail)
+{
+    // Attempting to construct a DescriptorSPKM that cannot be topped up (hardened derivation without private keys)
+    // should throw even though it is valid and can be parsed
+    CExtKey extkey;
+    extkey.SetSeed(std::array<std::byte, 32>{});
+    CWallet keystore(m_node.chain.get(), "", CreateMockableWalletDatabase());
+    BOOST_CHECK_EXCEPTION(
+        CreateDescriptor(keystore, "wpkh(" + EncodeExtPubKey(extkey.Neuter()) + "/*h)", /*success=*/true),
+        std::runtime_error, HasReason("Could not top up scriptPubKeys"));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 } // namespace wallet