diff --git a/runtime/fieldmask.go b/runtime/fieldmask.go
index 0138ed2f769..82ab3d277b2 100644
--- a/runtime/fieldmask.go
+++ b/runtime/fieldmask.go
@@ -53,7 +53,7 @@ func FieldMaskFromRequestBody(r io.Reader, msg proto.Message) (*field_mask.Field
 				}
 
 				if isDynamicProtoMessage(fd.Message()) {
-					for _, p := range buildPathsBlindly(k, v) {
+					for _, p := range buildPathsBlindly(string(fd.FullName().Name()), v) {
 						newPath := p
 						if item.path != "" {
 							newPath = item.path + "." + newPath
diff --git a/runtime/fieldmask_test.go b/runtime/fieldmask_test.go
index e458211a48e..fe3f0957968 100644
--- a/runtime/fieldmask_test.go
+++ b/runtime/fieldmask_test.go
@@ -60,6 +60,12 @@ func TestFieldMaskFromRequestBody(t *testing.T) {
 			input:    `{"struct_field": {"name":{"first": "bob"}, "amount": 2}}`,
 			expected: newFieldMask("struct_field.name.first", "struct_field.amount"),
 		},
+		{
+			name:     "NonStandardMessageWithJSONNamesForStruct",
+			msg:      &examplepb.NonStandardMessage{},
+			input:    `{"lineNum": 123, "structField": {"name":"bob"}}`,
+			expected: newFieldMask("line_num", "struct_field.name"),
+		},
 		{
 			name:     "value",
 			msg:      &examplepb.NonStandardMessage{},