diff --git a/nginx.go b/nginx.go
index 72b6d9d..139e395 100644
--- a/nginx.go
+++ b/nginx.go
@@ -30,7 +30,7 @@ func NewNginxExporter(accessLogPath string) (*NginxExporter, error) {
          prometheus.SummaryOpts{
             Namespace: Namespace,
             Subsystem: subsystem,
-            Name: "responses",
+            Name: "responses_sent_bytes",
             Help: "Summary of HTTP responses",
          },
          []string{"project", "network", "protocol"}),
@@ -38,7 +38,7 @@ func NewNginxExporter(accessLogPath string) (*NginxExporter, error) {
          prometheus.SummaryOpts{
             Namespace: Namespace,
             Subsystem: subsystem,
-            Name: "error_responses",
+            Name: "error_responses_sent_bytes",
             Help: "Summary of error HTTP responses",
          },
          []string{"project", "network", "protocol"}),
@@ -133,8 +133,11 @@ func (e *NginxExporter) processLogLine(line string) {
    // Increment totals
    e.responses.With(labels).Observe(size)
 
+   // Ensure an error version is created
+   errorObserver := e.error_responses.With(labels)
+
    if !success {
-      e.error_responses.With(labels).Observe(size)
+      errorObserver.Observe(size)
    }
 }
 
diff --git a/proftpd.go b/proftpd.go
index 863392d..7d02e7f 100644
--- a/proftpd.go
+++ b/proftpd.go
@@ -30,7 +30,7 @@ func NewProftpdExporter(transferLogPath string) (*ProftpdExporter, error) {
          prometheus.SummaryOpts{
             Namespace: Namespace,
             Subsystem: subsystem,
-            Name: "responses",
+            Name: "responses_sent_bytes",
             Help: "Summary of FTP responses",
          },
          []string{"project", "network", "protocol"}),
@@ -38,7 +38,7 @@ func NewProftpdExporter(transferLogPath string) (*ProftpdExporter, error) {
          prometheus.SummaryOpts{
             Namespace: Namespace,
             Subsystem: subsystem,
-            Name: "error_responses",
+            Name: "error_responses_sent_bytes",
             Help: "Summary of error FTP responses",
          },
          []string{"project", "network", "protocol"}),
@@ -121,10 +121,12 @@ func (e *ProftpdExporter) processLogLine(line string) {
    // Increment totals
    e.responses.With(labels).Observe(size)
 
-   if !success {
-      e.error_responses.With(labels).Observe(size)
-   }
+   // Ensure an error version is created
+   errorObserver := e.error_responses.With(labels)
 
+   if !success {
+      errorObserver.Observe(size)
+   }
 }
 
 func (e *ProftpdExporter) Monitor() {