diff --git a/zapcore/encoder.go b/zapcore/encoder.go
index 1bb684ae3..a1d46506f 100644
--- a/zapcore/encoder.go
+++ b/zapcore/encoder.go
@@ -107,7 +107,7 @@ func EpochNanosTimeEncoder(t time.Time, enc PrimitiveArrayEncoder) {
 // ISO8601TimeEncoder serializes a time.Time to an ISO8601-formatted string
 // with millisecond precision.
 func ISO8601TimeEncoder(t time.Time, enc PrimitiveArrayEncoder) {
-	enc.AppendString(t.Format("2006-01-02T15:04:05.999Z0700"))
+	enc.AppendString(t.Format("2006-01-02T15:04:05.000Z0700"))
 }
 
 // UnmarshalText unmarshals text to a TimeEncoder. "iso8601" and "ISO8601" are
diff --git a/zapcore/encoder_test.go b/zapcore/encoder_test.go
index 3f802d78c..d9af56688 100644
--- a/zapcore/encoder_test.go
+++ b/zapcore/encoder_test.go
@@ -403,17 +403,17 @@ func TestLevelEncoders(t *testing.T) {
 }
 
 func TestTimeEncoders(t *testing.T) {
-	moment := time.Unix(100, 5000500).UTC()
+	moment := time.Unix(100, 50005000).UTC()
 	tests := []struct {
 		name     string
 		expected interface{} // output of serializing moment
 	}{
-		{"iso8601", "1970-01-01T00:01:40.005Z"},
-		{"ISO8601", "1970-01-01T00:01:40.005Z"},
-		{"millis", 100005.0005},
-		{"nanos", int64(100005000500)},
-		{"", 100.0050005},
-		{"something-random", 100.0050005},
+		{"iso8601", "1970-01-01T00:01:40.050Z"},
+		{"ISO8601", "1970-01-01T00:01:40.050Z"},
+		{"millis", 100050.005},
+		{"nanos", int64(100050005000)},
+		{"", 100.050005},
+		{"something-random", 100.050005},
 	}
 
 	for _, tt := range tests {