diff --git a/src/keystore.cpp b/src/keystore.cpp
index 251e47e26..f32ba0c32 100644
--- a/src/keystore.cpp
+++ b/src/keystore.cpp
@@ -89,6 +89,6 @@ bool CBasicKeyStore::AddSpendingKey(const libzcash::SpendingKey &sk)
     LOCK(cs_SpendingKeyStore);
     auto address = sk.address();
     mapSpendingKeys[address] = sk;
-    mapNoteDecryptors[address] = ZCNoteDecryption(sk.viewing_key());
+    mapNoteDecryptors.insert(std::make_pair(address, ZCNoteDecryption(sk.viewing_key())));
     return true;
 }
diff --git a/src/wallet/gtest/test_wallet.cpp b/src/wallet/gtest/test_wallet.cpp
index cf418a596..289bd265f 100644
--- a/src/wallet/gtest/test_wallet.cpp
+++ b/src/wallet/gtest/test_wallet.cpp
@@ -172,7 +172,7 @@ TEST(wallet_tests, set_invalid_note_addrs_in_cwallettx) {
     CNoteData nd {sk.address(), uint256()};
     noteData[jsoutpt] = nd;
 
-    EXPECT_THROW(wtx.SetNoteData(noteData), std::runtime_error);
+    EXPECT_THROW(wtx.SetNoteData(noteData), std::logic_error);
 }
 
 TEST(wallet_tests, find_note_in_tx) {
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 438de40db..3407df53e 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -601,6 +601,8 @@ void CWallet::IncrementNoteWitnesses(const CBlockIndex* pindex,
         for (std::pair<const uint256, CWalletTx>& wtxItem : mapWallet) {
             for (mapNoteData_t::value_type& item : wtxItem.second.mapNoteData) {
                 CNoteData* nd = &(item.second);
+                // Check the validity of the cache
+                assert(nWitnessCacheSize >= nd->witnesses.size());
                 // Copy the witness for the previous block if we have one
                 if (nd->witnesses.size() > 0) {
                     nd->witnesses.push_front(nd->witnesses.front());
@@ -1060,8 +1062,12 @@ mapNoteData_t CWallet::FindMyNotes(const CTransaction& tx) const
                     CNoteData nd {address, note.nullifier(key)};
                     noteData.insert(std::make_pair(jsoutpt, nd));
                     break;
-                } catch (const std::exception &) {
+                } catch (const std::runtime_error &) {
                     // Couldn't decrypt with this spending key
+                } catch (const std::exception &exc) {
+                    // Unexpected failure
+                    LogPrintf("FindMyNotes(): Unexpected error while testing decrypt:\n");
+                    LogPrintf("%s\n", exc.what());
                 }
             }
         }
@@ -1252,7 +1258,7 @@ void CWalletTx::SetNoteData(mapNoteData_t &noteData)
         } else {
             // If FindMyNotes() was used to obtain noteData,
             // this should never happen
-            throw std::runtime_error("CWalletTc::SetNoteData(): Invalid note");
+            throw std::logic_error("CWalletTx::SetNoteData(): Invalid note");
         }
     }
 }
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 7fa88ab1d..b1c816fac 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -55,7 +55,8 @@ static const CAmount nHighTransactionMaxFeeWarning = 100 * nHighTransactionFeeWa
 //! Largest (in bytes) free transaction we're willing to create
 static const unsigned int MAX_FREE_TRANSACTION_CREATE_SIZE = 1000;
 //! Size of witness cache
-//  Should be large enough that we can expect to never reorg beyond our cache.
+//  Should be large enough that we can expect not to reorg beyond our cache
+//  unless there is some exceptional network disruption.
 static const unsigned int WITNESS_CACHE_SIZE = COINBASE_MATURITY;
 
 class CAccountingEntry;
diff --git a/src/zcash/Address.hpp b/src/zcash/Address.hpp
index d967aef27..58caae772 100644
--- a/src/zcash/Address.hpp
+++ b/src/zcash/Address.hpp
@@ -23,8 +23,13 @@ public:
         READWRITE(pk_enc);
     }
 
-    friend inline bool operator==(const PaymentAddress& a, const PaymentAddress& b) { return a.a_pk == b.a_pk && a.pk_enc == b.pk_enc; }
-    friend inline bool operator<(const PaymentAddress& a, const PaymentAddress& b) { return a.a_pk < b.a_pk; }
+    friend inline bool operator==(const PaymentAddress& a, const PaymentAddress& b) {
+        return a.a_pk == b.a_pk && a.pk_enc == b.pk_enc;
+    }
+    friend inline bool operator<(const PaymentAddress& a, const PaymentAddress& b) {
+        return (a.a_pk < b.a_pk ||
+                (a.a_pk == b.a_pk && a.pk_enc < b.pk_enc));
+    }
 };
 
 class ViewingKey : public uint256 {
diff --git a/src/zcash/NoteEncryption.hpp b/src/zcash/NoteEncryption.hpp
index bfeb80efa..e1f3718b0 100644
--- a/src/zcash/NoteEncryption.hpp
+++ b/src/zcash/NoteEncryption.hpp
@@ -61,7 +61,6 @@ public:
     typedef boost::array<unsigned char, CLEN> Ciphertext;
     typedef boost::array<unsigned char, MLEN> Plaintext;
 
-    // Unused default constructor to make allocators happy
     NoteDecryption() { }
     NoteDecryption(uint256 sk_enc);
 
@@ -71,8 +70,13 @@ public:
                       unsigned char nonce
                      ) const;
 
-    friend inline bool operator==(const NoteDecryption& a, const NoteDecryption& b) { return a.sk_enc == b.sk_enc && a.pk_enc == b.pk_enc; }
-    friend inline bool operator<(const NoteDecryption& a, const NoteDecryption& b) { return a.pk_enc < b.pk_enc; }
+    friend inline bool operator==(const NoteDecryption& a, const NoteDecryption& b) {
+        return a.sk_enc == b.sk_enc && a.pk_enc == b.pk_enc;
+    }
+    friend inline bool operator<(const NoteDecryption& a, const NoteDecryption& b) {
+        return (a.sk_enc < b.sk_enc ||
+                (a.sk_enc == b.sk_enc && a.pk_enc < b.pk_enc));
+    }
 };
 
 uint256 random_uint256();