diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -53,6 +53,22 @@
     return avoid_reuse;
 }
 
+/**
+ * Used by RPC commands that have an include_watchonly parameter. We default to
+ * true for watchonly wallets if include_watchonly isn't explicitly set.
+ */
+static bool ParseIncludeWatchonly(const UniValue &include_watchonly,
+                                  const CWallet &pwallet) {
+    if (include_watchonly.isNull()) {
+        // if include_watchonly isn't explicitly set, then check if we have a
+        // watchonly wallet
+        return pwallet.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
+    }
+
+    // otherwise return whatever include_watchonly was set to
+    return include_watchonly.get_bool();
+}
+
 /**
  * Checks if a CKey is in the given CWallet compressed or otherwise
  */
@@ -848,10 +864,7 @@
         min_depth = request.params[1].get_int();
     }
 
-    bool include_watchonly = false;
-    if (!request.params[2].isNull() && request.params[2].get_bool()) {
-        include_watchonly = true;
-    }
+    bool include_watchonly = ParseIncludeWatchonly(request.params[2], *pwallet);
 
     bool avoid_reuse = GetAvoidReuseFlag(pwallet, request.params[3]);
 
@@ -1183,8 +1196,8 @@
     }
 
     isminefilter filter = ISMINE_SPENDABLE;
-    if (!params[2].isNull() && params[2].get_bool()) {
-        filter = filter | ISMINE_WATCH_ONLY;
+    if (ParseIncludeWatchonly(params[2], *pwallet)) {
+        filter |= ISMINE_WATCH_ONLY;
     }
 
     bool has_filtered_address = false;
@@ -1646,8 +1659,8 @@
     }
 
     isminefilter filter = ISMINE_SPENDABLE;
-    if (!request.params[3].isNull() && request.params[3].get_bool()) {
-        filter = filter | ISMINE_WATCH_ONLY;
+    if (ParseIncludeWatchonly(request.params[3], *pwallet)) {
+        filter |= ISMINE_WATCH_ONLY;
     }
 
     if (nCount < 0) {
@@ -1838,8 +1851,8 @@
         }
     }
 
-    if (!request.params[2].isNull() && request.params[2].get_bool()) {
-        filter = filter | ISMINE_WATCH_ONLY;
+    if (ParseIncludeWatchonly(request.params[2], *pwallet)) {
+        filter |= ISMINE_WATCH_ONLY;
     }
 
     bool include_removed =
@@ -1992,8 +2005,8 @@
     TxId txid(ParseHashV(request.params[0], "txid"));
 
     isminefilter filter = ISMINE_SPENDABLE;
-    if (!request.params[1].isNull() && request.params[1].get_bool()) {
-        filter = filter | ISMINE_WATCH_ONLY;
+    if (ParseIncludeWatchonly(request.params[1], *pwallet)) {
+        filter |= ISMINE_WATCH_ONLY;
     }
 
     UniValue entry(UniValue::VOBJ);
@@ -3548,10 +3561,8 @@
                 change_position = options["changePosition"].get_int();
             }
 
-            if (options.exists("includeWatching")) {
-                coinControl.fAllowWatchOnly =
-                    options["includeWatching"].get_bool();
-            }
+            coinControl.fAllowWatchOnly =
+                ParseIncludeWatchonly(options["includeWatching"], *pwallet);
 
             if (options.exists("lockUnspents")) {
                 lockUnspents = options["lockUnspents"].get_bool();
@@ -3568,6 +3579,10 @@
                     options["subtractFeeFromOutputs"].get_array();
             }
         }
+    } else {
+        // if options is null and not a bool
+        coinControl.fAllowWatchOnly =
+            ParseIncludeWatchonly(NullUniValue, *pwallet);
     }
 
     if (tx.vout.size() == 0) {