diff --git a/.rubocop.yml b/.rubocop.yml
index a2f9efe1a..be78ea0dd 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -28,6 +28,10 @@ Style/SpecialGlobalVars:
 Style/FormatStringToken:
   Enabled: false
 
+# Due to Opal
+Style/SlicingWithRange:
+  Enabled: false
+
 Layout/EndOfLine:
   EnforcedStyle: lf
 
diff --git a/lib/bcdice/base.rb b/lib/bcdice/base.rb
index 566926e3c..1ab62a7d6 100644
--- a/lib/bcdice/base.rb
+++ b/lib/bcdice/base.rb
@@ -252,7 +252,7 @@ def dice_command(command)
       end
 
       secret = !m[1].nil?
-      command = command[1..] if secret # 先頭の 'S' をとる
+      command = command[1..-1] if secret # 先頭の 'S' をとる
 
       output = eval_game_system_specific_command(command)
 
diff --git a/lib/bcdice/game_system/BattleTech.rb b/lib/bcdice/game_system/BattleTech.rb
index af441ac6e..7d8094a94 100644
--- a/lib/bcdice/game_system/BattleTech.rb
+++ b/lib/bcdice/game_system/BattleTech.rb
@@ -364,7 +364,7 @@ def execute_ppc(parse_result)
         # TODO: 攻撃を表すクラスに変える
 
         # "PPC" 以降の部位指定
-        side = parse_result.command[3..]
+        side = parse_result.command[3..-1]
 
         modifier = Format.modifier(parse_result.modify_number)
         target = parse_result.target_number
diff --git a/lib/bcdice/game_system/DesperateRun.rb b/lib/bcdice/game_system/DesperateRun.rb
index 042c8b729..269ba3d7b 100644
--- a/lib/bcdice/game_system/DesperateRun.rb
+++ b/lib/bcdice/game_system/DesperateRun.rb
@@ -123,7 +123,7 @@ def check_roll(string)
         d1, d2 = @randomizer.roll_barabara(2, 6)
         dice_total = d1 + d2
         total = d1 + d2 + cmd.modify_number
-        target = cmd.command[2..].to_i
+        target = cmd.command[2..-1].to_i
 
         modifier_str = "　修正値：#{cmd.modify_number}" if cmd.modify_number != 0
 
diff --git a/lib/bcdice/game_system/SkynautsBouken.rb b/lib/bcdice/game_system/SkynautsBouken.rb
index 62a6c2c75..7fab218c4 100644
--- a/lib/bcdice/game_system/SkynautsBouken.rb
+++ b/lib/bcdice/game_system/SkynautsBouken.rb
@@ -106,7 +106,7 @@ def command_sn(command)
         debug("SN Parsed", dice_count, target, fumble)
 
         dice_list = @randomizer.roll_barabara(dice_count, 6)
-        dice_top_two = dice_list.sort[-2..]
+        dice_top_two = dice_list.sort[-2..-1]
         res = if dice_top_two == [6, 6]
                 Result.critical("スペシャル（【生命点】1d6回復）")
               elsif dice_list.max <= fumble
diff --git a/lib/bcdice/game_system/StellarKnights.rb b/lib/bcdice/game_system/StellarKnights.rb
index cef822fcc..bf457ba1b 100644
--- a/lib/bcdice/game_system/StellarKnights.rb
+++ b/lib/bcdice/game_system/StellarKnights.rb
@@ -149,7 +149,7 @@ def parse_dice_change_rules(text)
         return [] if text.nil?
 
         # 正規表現の都合で先頭に ',' が残っているので取っておく
-        text = text[1..]
+        text = text[1..-1]
         text.split(',').map do |rule|
           v = rule.split('>').map(&:to_i)
           {
diff --git a/lib/bcdice/game_system/TrinitySeven.rb b/lib/bcdice/game_system/TrinitySeven.rb
index 9491903c9..00082f67f 100644
--- a/lib/bcdice/game_system/TrinitySeven.rb
+++ b/lib/bcdice/game_system/TrinitySeven.rb
@@ -52,7 +52,7 @@ def roll_hit(command)
         cmd = parser.parse(command)
         return nil unless cmd
 
-        modify = cmd.command[2..].to_i + cmd.modify_number
+        modify = cmd.command[2..-1].to_i + cmd.modify_number
         critical = 7 + modify
         target = cmd.target_number