diff --git a/src/pkg/json/decode.go b/src/pkg/json/decode.go
index 4f6562bd552..6782c76c4e8 100644
--- a/src/pkg/json/decode.go
+++ b/src/pkg/json/decode.go
@@ -486,7 +486,7 @@ func (d *decodeState) object(v reflect.Value) {
 			if isValidTag(key) {
 				for i := 0; i < sv.NumField(); i++ {
 					f = st.Field(i)
-					if f.Tag.Get("json") == key {
+					if tagName(f.Tag.Get("json")) == key {
 						ok = true
 						break
 					}
@@ -918,3 +918,13 @@ func unquoteBytes(s []byte) (t []byte, ok bool) {
 	}
 	return b[0:w], true
 }
+
+// tagName extracts the field name part out of the "json" struct tag
+// value. The json struct tag format is an optional name, followed by
+// zero or more ",option" values.
+func tagName(v string) string {
+	if idx := strings.Index(v, ","); idx != -1 {
+		return v[:idx]
+	}
+	return v
+}
diff --git a/src/pkg/json/decode_test.go b/src/pkg/json/decode_test.go
index a855d604866..4c179de5d06 100644
--- a/src/pkg/json/decode_test.go
+++ b/src/pkg/json/decode_test.go
@@ -262,7 +262,8 @@ type All struct {
 	Float32 float32
 	Float64 float64
 
-	Foo string `json:"bar"`
+	Foo  string `json:"bar"`
+	Foo2 string `json:"bar2,dummyopt"`
 
 	PBool    *bool
 	PInt     *int
@@ -331,6 +332,7 @@ var allValue = All{
 	Float32: 14.1,
 	Float64: 15.1,
 	Foo:     "foo",
+	Foo2:    "foo2",
 	String:  "16",
 	Map: map[string]Small{
 		"17": {Tag: "tag17"},
@@ -391,6 +393,7 @@ var allValueIndent = `{
 	"Float32": 14.1,
 	"Float64": 15.1,
 	"bar": "foo",
+	"bar2": "foo2",
 	"PBool": null,
 	"PInt": null,
 	"PInt8": null,
@@ -481,6 +484,7 @@ var pallValueIndent = `{
 	"Float32": 0,
 	"Float64": 0,
 	"bar": "",
+	"bar2": "",
 	"PBool": true,
 	"PInt": 2,
 	"PInt8": 3,