diff --git a/src/Smdn.Fundamental.FourCC/Smdn/FourCC.cs b/src/Smdn.Fundamental.FourCC/Smdn/FourCC.cs
index 9c94719f4..4a713fa3f 100644
--- a/src/Smdn.Fundamental.FourCC/Smdn/FourCC.cs
+++ b/src/Smdn.Fundamental.FourCC/Smdn/FourCC.cs
@@ -192,7 +192,7 @@ public bool Equals(FourCC other)
     => other.fourcc == this.fourcc;
 
   public bool Equals(string other)
-    => string.Equals(this.ToString(), other);
+    => string.Equals(this.ToString(), other, StringComparison.Ordinal);
 
   public bool Equals(byte[] other)
     => (other != null) && other.SequenceEqual(this.ToByteArray());
diff --git a/src/Smdn.Fundamental.Shell/Smdn.OperatingSystem/ShellString.cs b/src/Smdn.Fundamental.Shell/Smdn.OperatingSystem/ShellString.cs
index bf3a57dda..b8b7f0ec1 100644
--- a/src/Smdn.Fundamental.Shell/Smdn.OperatingSystem/ShellString.cs
+++ b/src/Smdn.Fundamental.Shell/Smdn.OperatingSystem/ShellString.cs
@@ -79,7 +79,7 @@ public bool Equals(string other)
     if (other == null)
       return false;
     else
-      return string.Equals(this.Raw, other) || string.Equals(this.Expanded, other);
+      return string.Equals(this.Raw, other, StringComparison.Ordinal) || string.Equals(this.Expanded, other, StringComparison.Ordinal);
   }
 
   public static bool operator ==(ShellString x, ShellString y)
@@ -91,7 +91,7 @@ public bool Equals(string other)
         return false;
     }
 
-    return string.Equals(x.Expanded, y.Expanded);
+    return string.Equals(x.Expanded, y.Expanded, StringComparison.Ordinal);
   }
 
   public static bool operator !=(ShellString x, ShellString y) => !(x == y);