diff --git a/pkg/middlewares/accesslog/logger.go b/pkg/middlewares/accesslog/logger.go
index cf729c6de..ed85a8888 100644
--- a/pkg/middlewares/accesslog/logger.go
+++ b/pkg/middlewares/accesslog/logger.go
@@ -105,15 +105,28 @@ func NewHandler(config *types.AccessLog) (*Handler, error) {
 		Level:     logrus.InfoLevel,
 	}
 
-	// Transform headers names in config to a canonical form, to be used as is without further transformations.
-	if config.Fields != nil && config.Fields.Headers != nil && len(config.Fields.Headers.Names) > 0 {
-		fields := map[string]string{}
+	// Transform header names to a canonical form, to be used as is without further transformations,
+	// and transform field names to lower case, to enable case-insensitive lookup.
+	if config.Fields != nil {
+		if len(config.Fields.Names) > 0 {
+			fields := map[string]string{}
 
-		for h, v := range config.Fields.Headers.Names {
-			fields[textproto.CanonicalMIMEHeaderKey(h)] = v
+			for h, v := range config.Fields.Names {
+				fields[strings.ToLower(h)] = v
+			}
+
+			config.Fields.Names = fields
 		}
 
-		config.Fields.Headers.Names = fields
+		if config.Fields.Headers != nil && len(config.Fields.Headers.Names) > 0 {
+			fields := map[string]string{}
+
+			for h, v := range config.Fields.Headers.Names {
+				fields[textproto.CanonicalMIMEHeaderKey(h)] = v
+			}
+
+			config.Fields.Headers.Names = fields
+		}
 	}
 
 	logHandler := &Handler{
@@ -332,7 +345,7 @@ func (h *Handler) logTheRoundTrip(logDataTable *LogData) {
 		fields := logrus.Fields{}
 
 		for k, v := range logDataTable.Core {
-			if h.config.Fields.Keep(k) {
+			if h.config.Fields.Keep(strings.ToLower(k)) {
 				fields[k] = v
 			}
 		}
diff --git a/pkg/middlewares/accesslog/logger_test.go b/pkg/middlewares/accesslog/logger_test.go
index 338467293..46563db61 100644
--- a/pkg/middlewares/accesslog/logger_test.go
+++ b/pkg/middlewares/accesslog/logger_test.go
@@ -462,6 +462,32 @@ func TestLoggerJSON(t *testing.T) {
 				RequestRefererHeader: assertString(testReferer),
 			},
 		},
+		{
+			desc: "fields and headers with unconventional letter case",
+			config: &types.AccessLog{
+				FilePath: "",
+				Format:   JSONFormat,
+				Fields: &types.AccessLogFields{
+					DefaultMode: "drop",
+					Names: map[string]string{
+						"rEqUeStHoSt": "keep",
+					},
+					Headers: &types.FieldHeaders{
+						DefaultMode: "drop",
+						Names: map[string]string{
+							"ReFeReR": "keep",
+						},
+					},
+				},
+			},
+			expected: map[string]func(t *testing.T, value interface{}){
+				RequestHost:          assertString(testHostname),
+				"level":              assertString("info"),
+				"msg":                assertString(""),
+				"time":               assertNotEmpty(),
+				RequestRefererHeader: assertString(testReferer),
+			},
+		},
 	}
 
 	for _, test := range testCases {