diff --git a/decode.go b/decode.go
index 2cb7a44f..b0990c8e 100644
--- a/decode.go
+++ b/decode.go
@@ -34,6 +34,7 @@ type Decoder struct {
 	isResolvedReference  bool
 	validator            StructValidator
 	disallowUnknownField bool
+	disallowDuplicateKey bool
 	useOrderedMap        bool
 	parsedFile           *ast.File
 	streamIndex          int
@@ -52,6 +53,7 @@ func NewDecoder(r io.Reader, opts ...DecodeOption) *Decoder {
 		isRecursiveDir:       false,
 		isResolvedReference:  false,
 		disallowUnknownField: false,
+		disallowDuplicateKey: false,
 		useOrderedMap:        false,
 	}
 }
@@ -347,6 +349,18 @@ func errUnknownField(msg string, tk *token.Token) *unknownFieldError {
 	return &unknownFieldError{err: errors.ErrSyntax(msg, tk)}
 }
 
+type duplicateKeyError struct {
+	err error
+}
+
+func (e *duplicateKeyError) Error() string {
+	return e.err.Error()
+}
+
+func errDuplicateKey(msg string, tk *token.Token) *duplicateKeyError {
+	return &duplicateKeyError{err: errors.ErrSyntax(msg, tk)}
+}
+
 func (d *Decoder) deleteStructKeys(structValue reflect.Value, unknownFields map[string]ast.Node) error {
 	strType := structValue.Type()
 	structFieldMap, err := structFieldMap(strType)
@@ -953,6 +967,20 @@ func (d *Decoder) decodeMapItem(dst *MapItem, src ast.Node) error {
 	return nil
 }
 
+func (d *Decoder) validateMapKey(keyMap map[string]struct{}, key interface{}, keyNode ast.Node) error {
+	k, ok := key.(string)
+	if !ok {
+		return nil
+	}
+	if d.disallowDuplicateKey {
+		if _, exists := keyMap[k]; exists {
+			return errDuplicateKey(fmt.Sprintf(`duplicate key "%s"`, k), keyNode.GetToken())
+		}
+	}
+	keyMap[k] = struct{}{}
+	return nil
+}
+
 func (d *Decoder) decodeMapSlice(dst *MapSlice, src ast.Node) error {
 	mapNode, err := d.getMapNode(src)
 	if err != nil {
@@ -963,6 +991,7 @@ func (d *Decoder) decodeMapSlice(dst *MapSlice, src ast.Node) error {
 	}
 	mapSlice := MapSlice{}
 	mapIter := mapNode.MapRange()
+	keyMap := map[string]struct{}{}
 	for mapIter.Next() {
 		key := mapIter.Key()
 		value := mapIter.Value()
@@ -972,12 +1001,19 @@ func (d *Decoder) decodeMapSlice(dst *MapSlice, src ast.Node) error {
 				return errors.Wrapf(err, "failed to decode map with merge key")
 			}
 			for _, v := range m {
+				if err := d.validateMapKey(keyMap, v.Key, value); err != nil {
+					return errors.Wrapf(err, "invalid map key")
+				}
 				mapSlice = append(mapSlice, v)
 			}
 			continue
 		}
+		k := d.nodeToValue(key)
+		if err := d.validateMapKey(keyMap, k, key); err != nil {
+			return errors.Wrapf(err, "invalid map key")
+		}
 		mapSlice = append(mapSlice, MapItem{
-			Key:   d.nodeToValue(key),
+			Key:   k,
 			Value: d.nodeToValue(value),
 		})
 	}
@@ -998,6 +1034,7 @@ func (d *Decoder) decodeMap(dst reflect.Value, src ast.Node) error {
 	keyType := mapValue.Type().Key()
 	valueType := mapValue.Type().Elem()
 	mapIter := mapNode.MapRange()
+	keyMap := map[string]struct{}{}
 	var foundErr error
 	for mapIter.Next() {
 		key := mapIter.Key()
@@ -1008,6 +1045,9 @@ func (d *Decoder) decodeMap(dst reflect.Value, src ast.Node) error {
 			}
 			iter := dst.MapRange()
 			for iter.Next() {
+				if err := d.validateMapKey(keyMap, iter.Key(), value); err != nil {
+					return errors.Wrapf(err, "invalid map key")
+				}
 				mapValue.SetMapIndex(iter.Key(), iter.Value())
 			}
 			continue
@@ -1016,6 +1056,11 @@ func (d *Decoder) decodeMap(dst reflect.Value, src ast.Node) error {
 		if k.IsValid() && k.Type().ConvertibleTo(keyType) {
 			k = k.Convert(keyType)
 		}
+		if k.IsValid() {
+			if err := d.validateMapKey(keyMap, k.Interface(), key); err != nil {
+				return errors.Wrapf(err, "invalid map key")
+			}
+		}
 		if valueType.Kind() == reflect.Ptr && value.Type() == ast.NullType {
 			// set nil value to pointer
 			mapValue.SetMapIndex(k, reflect.Zero(valueType))
diff --git a/decode_test.go b/decode_test.go
index 86792195..ab5757f2 100644
--- a/decode_test.go
+++ b/decode_test.go
@@ -1438,6 +1438,26 @@ children:
 	})
 }
 
+func TestDecoder_DisallowDuplicateKey(t *testing.T) {
+	yml := `
+a: b
+a: c
+`
+	expected := `
+[3:1] duplicate key "a"
+   2 | 
+>  3 | a: b
+   4 | a: c
+      ^
+`
+	var v map[string]string
+	err := yaml.NewDecoder(strings.NewReader(yml), yaml.DisallowDuplicateKey()).Decode(&v)
+	actual := "\n" + err.Error()
+	if expected != actual {
+		t.Fatalf("expected:[%s] actual:[%s]", expected, actual)
+	}
+}
+
 func TestDecoder_DefaultValues(t *testing.T) {
 	v := struct {
 		A string `yaml:"a"`
diff --git a/option.go b/option.go
index b81ed116..1b40f3eb 100644
--- a/option.go
+++ b/option.go
@@ -49,6 +49,15 @@ func Validator(v StructValidator) DecodeOption {
 	}
 }
 
+// Strict enable DisallowUnknownField and DisallowDuplicateKey
+func Strict() DecodeOption {
+	return func(d *Decoder) error {
+		d.disallowUnknownField = true
+		d.disallowDuplicateKey = true
+		return nil
+	}
+}
+
 // DisallowUnknownField causes the Decoder to return an error when the destination
 // is a struct and the input contains object keys which do not match any
 // non-ignored, exported fields in the destination.
@@ -59,6 +68,14 @@ func DisallowUnknownField() DecodeOption {
 	}
 }
 
+// DisallowDuplicateKey causes an error when mapping keys that are duplicates
+func DisallowDuplicateKey() DecodeOption {
+	return func(d *Decoder) error {
+		d.disallowDuplicateKey = true
+		return nil
+	}
+}
+
 // UseOrderedMap can be interpreted as a map,
 // and uses MapSlice ( ordered map ) aggressively if there is no type specification
 func UseOrderedMap() DecodeOption {