diff --git a/prometheus/http.go b/prometheus/http.go
index 3d47a81..4d08154 100644
--- a/prometheus/http.go
+++ b/prometheus/http.go
@@ -115,7 +115,7 @@ func decorateWriter(request *http.Request, writer io.Writer) (io.Writer, string)
 	header := request.Header.Get(acceptEncodingHeader)
 	parts := strings.Split(header, ",")
 	for _, part := range parts {
-		part := strings.TrimSpace(part)
+		part = strings.TrimSpace(part)
 		if part == "gzip" || strings.HasPrefix(part, "gzip;") {
 			return gzip.NewWriter(writer), "gzip"
 		}
diff --git a/prometheus/http_test.go b/prometheus/http_test.go
index edd47ad..dd89ccf 100644
--- a/prometheus/http_test.go
+++ b/prometheus/http_test.go
@@ -47,9 +47,9 @@ func TestInstrumentHandler(t *testing.T) {
 	instant := time.Now()
 	end := instant.Add(30 * time.Second)
 	now = nowSeries(instant, end)
-	respBody := respBody("Howdy there!")
+	body := respBody("Howdy there!")
 
-	hndlr := InstrumentHandler("test-handler", respBody)
+	hndlr := InstrumentHandler("test-handler", body)
 
 	opts := SummaryOpts{
 		Subsystem:   "http",
diff --git a/prometheus/promhttp/http.go b/prometheus/promhttp/http.go
index 8dc2603..0135737 100644
--- a/prometheus/promhttp/http.go
+++ b/prometheus/promhttp/http.go
@@ -302,7 +302,7 @@ func decorateWriter(request *http.Request, writer io.Writer, compressionDisabled
 	header := request.Header.Get(acceptEncodingHeader)
 	parts := strings.Split(header, ",")
 	for _, part := range parts {
-		part := strings.TrimSpace(part)
+		part = strings.TrimSpace(part)
 		if part == "gzip" || strings.HasPrefix(part, "gzip;") {
 			return gzip.NewWriter(writer), "gzip"
 		}