diff --git a/sortix/device.h b/sortix/device.h
index 477d56ce..35204246 100644
--- a/sortix/device.h
+++ b/sortix/device.h
@@ -49,7 +49,7 @@ namespace Sortix
 		void Unref();
 
 	public:
-		virtual bool IsType(unsigned type) = 0;
+		virtual bool IsType(unsigned type) const = 0;
 
 	};
 }
diff --git a/sortix/directory.h b/sortix/directory.h
index 8f0bd6a3..4dfa7381 100644
--- a/sortix/directory.h
+++ b/sortix/directory.h
@@ -50,7 +50,7 @@ namespace Sortix
 		virtual int Read(sortix_dirent* dirent, size_t available) = 0;
 
 	public:
-		virtual bool IsType(unsigned type) { return type == Device::DIRECTORY; }
+		virtual bool IsType(unsigned type) const { return type == Device::DIRECTORY; }
 
 	};
 
diff --git a/sortix/filesystem.h b/sortix/filesystem.h
index 84920f7c..e4a4a8a8 100644
--- a/sortix/filesystem.h
+++ b/sortix/filesystem.h
@@ -58,7 +58,7 @@ namespace Sortix
 		virtual bool Unlink(const char* path) = 0;
 
 	public:
-		virtual bool IsType(unsigned type) { return type == Device::FILESYSTEM; }
+		virtual bool IsType(unsigned type) const { return type == Device::FILESYSTEM; }
 
 	};
 
diff --git a/sortix/fs/devfs.cpp b/sortix/fs/devfs.cpp
index 3fcf9f9f..d6dde43e 100644
--- a/sortix/fs/devfs.cpp
+++ b/sortix/fs/devfs.cpp
@@ -163,7 +163,7 @@ namespace Sortix
 		virtual ssize_t Write(const byte* src, size_t count);
 		virtual bool IsReadable();
 		virtual bool IsWritable();
-		virtual bool IsType(unsigned type);
+		virtual bool IsType(unsigned type) const;
 
 	};
 	
@@ -199,7 +199,7 @@ namespace Sortix
 		return true;
 	}
 
-	bool DevLogTTY::IsType(unsigned type)
+	bool DevLogTTY::IsType(unsigned type) const
 	{
 		return type == Device::TTY || BaseClass::IsType(type);
 	}
diff --git a/sortix/stream.h b/sortix/stream.h
index d4e751bb..e5b85c17 100644
--- a/sortix/stream.h
+++ b/sortix/stream.h
@@ -35,7 +35,7 @@ namespace Sortix
 		typedef Device BaseClass;
 
 	public:
-		virtual bool IsType(unsigned type) { return type == Device::STREAM; }
+		virtual bool IsType(unsigned type) const { return type == Device::STREAM; }
 
 	public:
 		virtual ssize_t Read(byte* dest, size_t count) = 0;
@@ -51,7 +51,7 @@ namespace Sortix
 		typedef DevStream BaseClass;
 
 	public:
-		virtual bool IsType(unsigned type)
+		virtual bool IsType(unsigned type) const
 		{
 			return type == Device::BUFFER || BaseClass::IsType(type);
 		}