diff --git a/ojosama_test.go b/ojosama_test.go
index c01887f..e26b5a8 100644
--- a/ojosama_test.go
+++ b/ojosama_test.go
@@ -341,6 +341,13 @@ func TestConvert(t *testing.T) {
 			opt:     nil,
 			wantErr: false,
 		},
+		{
+			desc:    "正常系: 罵倒には「お」を付けませんのよ",
+			src:     "カス",
+			want:    "カス",
+			opt:     nil,
+			wantErr: false,
+		},
 	}
 
 	for _, tt := range tests {
diff --git a/rule.go b/rule.go
index fd412fa..8c8c251 100644
--- a/rule.go
+++ b/rule.go
@@ -257,6 +257,18 @@ var (
 				},
 			},
 		},
+		{
+			Conditions: []convertCondition{
+				{
+					Type:  convertTypeFeatures,
+					Value: []string{"名詞", "固有名詞", "一般"},
+				},
+				{
+					Type:  convertTypeSurface,
+					Value: []string{"カス"},
+				},
+			},
+		},
 	}
 
 	convertRules = []convertRule{