diff --git a/API-CHANGELOG.md b/API-CHANGELOG.md
index a04f2653285..e5df7b4f49e 100644
--- a/API-CHANGELOG.md
+++ b/API-CHANGELOG.md
@@ -53,6 +53,7 @@ This section contains changes targeting a future version.
 - `submit`: The `fail_hard` field now returns an error if the value is not a boolean. [#6529](https://github.com/XRPLF/rippled/pull/6529)
 - `subscribe`: The `taker` field in the `books` array now returns `actMalformed` instead of `badIssuer` if the value is not a valid account. [#6529](https://github.com/XRPLF/rippled/pull/6529)
 - Fixed a bug in `Forwarded` HTTP header parsing where the extracted IP address could be incorrect when no comma or semicolon delimiter follows the address. This could cause the server to misidentify a client's IP address when operating behind a reverse proxy. [#6529](https://github.com/XRPLF/rippled/pull/6529)
+- `tx_history`: The `start` field now returns `invalidParams` if the value is not a non-negative integer. Previously, values that could not be converted returned an `internal` error, and strings, booleans, and `null` were silently coerced. [#7891](https://github.com/XRPLF/rippled/pull/7891)
 
 ## XRP Ledger server version 3.1.0
 
diff --git a/src/test/rpc/TransactionHistory_test.cpp b/src/test/rpc/TransactionHistory_test.cpp
index 6227a1b75bb..e581cfe8892 100644
--- a/src/test/rpc/TransactionHistory_test.cpp
+++ b/src/test/rpc/TransactionHistory_test.cpp
@@ -42,6 +42,38 @@ class TransactionHistory_test : public beast::unit_test::Suite
             BEAST_EXPECT(result[jss::error] == "noPermission");
             BEAST_EXPECT(result[jss::status] == "error");
         }
+
+        {
+            // a malformed start must report invalidParams, not internal
+            json::Value objStart{json::ValueType::Object};
+            objStart["nope"] = 0;
+            json::Value arrStart{json::ValueType::Array};
+            arrStart.append(0);
+
+            // Note that a whole number beyond the range of a uint, e.g.
+            // 4294967296, is rejected by the json parser itself, so it never
+            // reaches the handler and is not covered here.
+            boost::container::static_vector<json::Value, 9> const badStarts{
+                json::Value{-1},     // negative
+                json::Value{"abc"},  // not a number
+                json::Value{"5"},    // numeric, but a string
+                json::Value{1.5},    // not a whole number
+                json::Value{1e30},   // beyond the range of a uint
+                json::Value{true},   // bool
+                json::Value{},       // null
+                objStart,
+                arrStart,
+            };
+
+            for (auto const& badStart : badStarts)
+            {
+                json::Value params{json::ValueType::Object};
+                params[jss::start] = badStart;
+                auto const result = env.client().invoke("tx_history", params)[jss::result];
+                BEAST_EXPECT(result[jss::error] == "invalidParams");
+                BEAST_EXPECT(result[jss::status] == "error");
+            }
+        }
     }
 
     void
diff --git a/src/xrpld/rpc/handlers/transaction/TxHistory.cpp b/src/xrpld/rpc/handlers/transaction/TxHistory.cpp
index a45046773cc..560cb3aa157 100644
--- a/src/xrpld/rpc/handlers/transaction/TxHistory.cpp
+++ b/src/xrpld/rpc/handlers/transaction/TxHistory.cpp
@@ -26,7 +26,14 @@ doTxHistory(RPC::JsonContext& context)
     if (!context.params.isMember(jss::start))
         return rpcError(RpcInvalidParams);
 
-    unsigned int const startIndex = context.params[jss::start].asUInt();
+    // Guard the conversion: json::Value::asUInt() throws for negative,
+    // out-of-range, non-numeric or non-scalar values, which would surface as a
+    // generic internal error instead of invalid parameters.
+    auto const& jvStart = context.params[jss::start];
+    if (!jvStart.isUInt() && (!jvStart.isInt() || jvStart.asInt() < 0))
+        return rpcError(RpcInvalidParams);
+
+    unsigned int const startIndex = jvStart.asUInt();
 
     if ((startIndex > 10000) && (!isUnlimited(context.role)))
         return rpcError(RpcNoPermission);