diff --git a/src/cmd/vet/main.go b/src/cmd/vet/main.go
index b317c88738..8149ba04e0 100644
--- a/src/cmd/vet/main.go
+++ b/src/cmd/vet/main.go
@@ -133,13 +133,13 @@ var (
 	callExpr      *ast.CallExpr
 	compositeLit  *ast.CompositeLit
 	exprStmt      *ast.ExprStmt
-	field         *ast.Field
 	funcDecl      *ast.FuncDecl
 	funcLit       *ast.FuncLit
 	genDecl       *ast.GenDecl
 	interfaceType *ast.InterfaceType
 	rangeStmt     *ast.RangeStmt
 	returnStmt    *ast.ReturnStmt
+	structType    *ast.StructType
 
 	// checkers is a two-level map.
 	// The outer level is keyed by a nil pointer, one of the AST vars above.
@@ -478,8 +478,6 @@ func (f *File) Visit(node ast.Node) ast.Visitor {
 		key = compositeLit
 	case *ast.ExprStmt:
 		key = exprStmt
-	case *ast.Field:
-		key = field
 	case *ast.FuncDecl:
 		key = funcDecl
 	case *ast.FuncLit:
@@ -492,6 +490,8 @@ func (f *File) Visit(node ast.Node) ast.Visitor {
 		key = rangeStmt
 	case *ast.ReturnStmt:
 		key = returnStmt
+	case *ast.StructType:
+		key = structType
 	}
 	for _, fn := range f.checkers[key] {
 		fn(f, node)
diff --git a/src/cmd/vet/structtag.go b/src/cmd/vet/structtag.go
index 8134c585b3..1b92aaf51b 100644
--- a/src/cmd/vet/structtag.go
+++ b/src/cmd/vet/structtag.go
@@ -9,20 +9,31 @@ package main
 import (
 	"errors"
 	"go/ast"
+	"go/token"
 	"reflect"
 	"strconv"
+	"strings"
 )
 
 func init() {
 	register("structtags",
 		"check that struct field tags have canonical format and apply to exported fields as needed",
-		checkCanonicalFieldTag,
-		field)
+		checkStructFieldTags,
+		structType)
 }
 
-// checkCanonicalFieldTag checks a struct field tag.
-func checkCanonicalFieldTag(f *File, node ast.Node) {
-	field := node.(*ast.Field)
+// checkStructFieldTags checks all the field tags of a struct, including checking for duplicates.
+func checkStructFieldTags(f *File, node ast.Node) {
+	var seen map[[2]string]token.Pos
+	for _, field := range node.(*ast.StructType).Fields.List {
+		checkCanonicalFieldTag(f, field, &seen)
+	}
+}
+
+var checkTagDups = []string{"json", "xml"}
+
+// checkCanonicalFieldTag checks a single struct field tag.
+func checkCanonicalFieldTag(f *File, field *ast.Field, seen *map[[2]string]token.Pos) {
 	if field.Tag == nil {
 		return
 	}
@@ -38,6 +49,24 @@ func checkCanonicalFieldTag(f *File, node ast.Node) {
 		f.Badf(field.Pos(), "struct field tag %q not compatible with reflect.StructTag.Get: %s", raw, err)
 	}
 
+	for _, key := range checkTagDups {
+		val := reflect.StructTag(tag).Get(key)
+		if val == "" || val == "-" || val[0] == ',' {
+			continue
+		}
+		if i := strings.Index(val, ","); i >= 0 {
+			val = val[:i]
+		}
+		if *seen == nil {
+			*seen = map[[2]string]token.Pos{}
+		}
+		if pos, ok := (*seen)[[2]string{key, val}]; ok {
+			f.Badf(field.Pos(), "struct field %s repeats %s tag %q also at %s", field.Names[0].Name, key, val, f.loc(pos))
+		} else {
+			(*seen)[[2]string{key, val}] = field.Pos()
+		}
+	}
+
 	// Check for use of json or xml tags with unexported fields.
 
 	// Embedded struct. Nothing to do for now, but that
@@ -50,9 +79,8 @@ func checkCanonicalFieldTag(f *File, node ast.Node) {
 		return
 	}
 
-	st := reflect.StructTag(tag)
 	for _, enc := range [...]string{"json", "xml"} {
-		if st.Get(enc) != "" {
+		if reflect.StructTag(tag).Get(enc) != "" {
 			f.Badf(field.Pos(), "struct field %s has %s tag but is not exported", field.Names[0].Name, enc)
 			return
 		}
diff --git a/src/cmd/vet/testdata/structtag.go b/src/cmd/vet/testdata/structtag.go
index 6878f5642d..74c7b541cb 100644
--- a/src/cmd/vet/testdata/structtag.go
+++ b/src/cmd/vet/testdata/structtag.go
@@ -34,3 +34,31 @@ type JSONEmbeddedField struct {
 	UnexportedEncodingTagTest `is:"embedded"`
 	unexp                     `is:"embedded,notexported" json:"unexp"` // OK for now, see issue 7363
 }
+
+type DuplicateJSONFields struct {
+	JSON              int `json:"a"`
+	DuplicateJSON     int `json:"a"` // ERROR "struct field DuplicateJSON repeats json tag .a. also at testdata/structtag.go:39"
+	IgnoredJSON       int `json:"-"`
+	OtherIgnoredJSON  int `json:"-"`
+	OmitJSON          int `json:",omitempty"`
+	OtherOmitJSON     int `json:",omitempty"`
+	DuplicateOmitJSON int `json:"a,omitempty"` // ERROR "struct field DuplicateOmitJSON repeats json tag .a. also at testdata/structtag.go:39"
+	NonJSON           int `foo:"a"`
+	DuplicateNonJSON  int `foo:"a"`
+	Embedded          struct {
+		DuplicateJSON int `json:"a"` // OK because its not in the same struct type
+	}
+
+	XML              int `xml:"a"`
+	DuplicateXML     int `xml:"a"` // ERROR "struct field DuplicateXML repeats xml tag .a. also at testdata/structtag.go:52"
+	IgnoredXML       int `xml:"-"`
+	OtherIgnoredXML  int `xml:"-"`
+	OmitXML          int `xml:",omitempty"`
+	OtherOmitXML     int `xml:",omitempty"`
+	DuplicateOmitXML int `xml:"a,omitempty"` // ERROR "struct field DuplicateOmitXML repeats xml tag .a. also at testdata/structtag.go:52"
+	NonXML           int `foo:"a"`
+	DuplicateNonXML  int `foo:"a"`
+	Embedded         struct {
+		DuplicateXML int `xml:"a"` // OK because its not in the same struct type
+	}
+}