diff --git a/src/rpc/util.h b/src/rpc/util.h
--- a/src/rpc/util.h
+++ b/src/rpc/util.h
@@ -116,8 +116,7 @@
 class RPCHelpMan {
 public:
     RPCHelpMan(const std::string &name, const std::string &description,
-               const std::vector<RPCArg> &args)
-        : m_name{name}, m_description{description}, m_args{args} {}
+               const std::vector<RPCArg> &args);
 
     std::string ToString() const;
 
diff --git a/src/rpc/util.cpp b/src/rpc/util.cpp
--- a/src/rpc/util.cpp
+++ b/src/rpc/util.cpp
@@ -283,6 +283,16 @@
     }
 };
 
+RPCHelpMan::RPCHelpMan(const std::string &name, const std::string &description,
+                       const std::vector<RPCArg> &args)
+    : m_name{name}, m_description{description}, m_args{args} {
+    std::set<std::string> named_args;
+    for (const auto &arg : m_args) {
+        // Should have unique named arguments
+        CHECK_NONFATAL(named_args.insert(arg.m_name).second);
+    }
+}
+
 std::string RPCHelpMan::ToString() const {
     std::string ret;