diff --git a/encoding/prototext/decode.go b/encoding/prototext/decode.go
index a7fc2bf..df05f95 100644
--- a/encoding/prototext/decode.go
+++ b/encoding/prototext/decode.go
@@ -95,9 +95,19 @@
 		case text.Name:
 			name, _ = tkey.Name()
 			fd = fieldDescs.ByName(name)
+			// The proto name of a group field is in all lowercase. However, the
+			// textproto field name is the type name. Check to make sure that
+			// group name is correct.
 			if fd == nil {
-				// Check if this is a group field.
-				fd = fieldDescs.ByName(pref.Name(strings.ToLower(string(name))))
+				gd := fieldDescs.ByName(pref.Name(strings.ToLower(string(name))))
+				if gd != nil && gd.Kind() == pref.GroupKind && gd.Message().Name() == name {
+					fd = gd
+				}
+			} else {
+				if fd.Kind() == pref.GroupKind && fd.Message().Name() != name {
+					// Reset fd to nil because name does not match.
+					fd = nil
+				}
 			}
 		case text.String:
 			// Handle extensions only. This code path is not for Any.
diff --git a/encoding/prototext/decode_test.go b/encoding/prototext/decode_test.go
index 32d9be8..7f0a4e8 100644
--- a/encoding/prototext/decode_test.go
+++ b/encoding/prototext/decode_test.go
@@ -121,6 +121,11 @@
 			OptString:   scalar.String("谷歌"),
 		},
 	}, {
+		desc:         "case sensitive",
+		inputMessage: &pb3.Scalars{},
+		inputText:    `S_BOOL: true`,
+		wantErr:      true,
+	}, {
 		desc:         "proto3 scalars",
 		inputMessage: &pb3.Scalars{},
 		inputText: `s_bool: true
@@ -404,6 +409,11 @@
 			Optgroup:  &pb2.Nests_OptGroup{},
 		},
 	}, {
+		desc:         "group field name",
+		inputMessage: &pb2.Nests{},
+		inputText:    `optgroup: {}`,
+		wantErr:      true,
+	}, {
 		desc:         "proto2 nested messages",
 		inputMessage: &pb2.Nests{},
 		inputText: `
diff --git a/internal/impl/message_test.go b/internal/impl/message_test.go
index fb89a2d..af7196d 100644
--- a/internal/impl/message_test.go
+++ b/internal/impl/message_test.go
@@ -990,8 +990,8 @@
 		field: [
 			{name:"f1"  number:1  label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".EnumProto2" default_value:"BEEF"},
 			{name:"f2"  number:2  label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".EnumProto3" default_value:"BRAVO"},
-			{name:"f3"  number:3  label:LABEL_OPTIONAL type:TYPE_MESSAGE type_Name:".google.golang.org.proto2_20180125.Message"},
-			{name:"f4"  number:4  label:LABEL_OPTIONAL type:TYPE_MESSAGE type_Name:".EnumMessages"},
+			{name:"f3"  number:3  label:LABEL_OPTIONAL type:TYPE_MESSAGE type_name:".google.golang.org.proto2_20180125.Message"},
+			{name:"f4"  number:4  label:LABEL_OPTIONAL type:TYPE_MESSAGE type_name:".EnumMessages"},
 			{name:"f5"  number:5  label:LABEL_REPEATED type:TYPE_ENUM    type_name:".EnumProto2"},
 			{name:"f6"  number:6  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".ScalarProto2"},
 			{name:"f7"  number:7  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".EnumMessages.F7Entry"},