diff --git a/rpc/endpoints.go b/rpc/endpoints.go
index 8ca6d4eb0c6d..e734f0c880b2 100644
--- a/rpc/endpoints.go
+++ b/rpc/endpoints.go
@@ -17,16 +17,49 @@
 package rpc
 
 import (
+	"fmt"
 	"net"
 
 	"github.com/ethereum/go-ethereum/log"
 )
 
+// checkModuleAvailable check that requested api modules (eg. via --rpcapi) are actually
+// available API services. If an invalid module is given (ie API "foo" wanted which does not exist),
+// then an error is returned including the invalid module and a list of available
+// API service names.
+func checkModuleAvailable(module string, apis []API) (err error) {
+	for _, api := range apis {
+		if module == api.Namespace {
+			return nil
+		}
+	}
+	// Module did not find a matching api namespace: this is an invalid module.
+	// Collect list of available modules for user debugging.
+	available := []string{}
+outer:
+	for _, api := range apis {
+
+		// Only include unique api names
+		for _, av := range available {
+			if av == api.Namespace {
+				continue outer
+			}
+		}
+		available = append(available, api.Namespace)
+	}
+	return fmt.Errorf("invalid api module: module=%s available=%v", module, available)
+}
+
 // StartHTTPEndpoint starts the HTTP RPC endpoint, configured with cors/vhosts/modules
 func StartHTTPEndpoint(endpoint string, apis []API, modules []string, cors []string, vhosts []string, timeouts HTTPTimeouts) (net.Listener, *Server, error) {
 	// Generate the whitelist based on the allowed modules
 	whitelist := make(map[string]bool)
 	for _, module := range modules {
+
+		// Ensure the requested module is actually available.
+		if err := checkModuleAvailable(module, apis); err != nil {
+			return nil, nil, err
+		}
 		whitelist[module] = true
 	}
 	// Register all the APIs exposed by the services
@@ -57,6 +90,11 @@ func StartWSEndpoint(endpoint string, apis []API, modules []string, wsOrigins []
 	// Generate the whitelist based on the allowed modules
 	whitelist := make(map[string]bool)
 	for _, module := range modules {
+
+		// Ensure the requested module is actually available.
+		if err := checkModuleAvailable(module, apis); err != nil {
+			return nil, nil, err
+		}
 		whitelist[module] = true
 	}
 	// Register all the APIs exposed by the services