diff --git a/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.cpp b/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.cpp
index 204cb236b0..52594bfe7d 100644
--- a/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.cpp
+++ b/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.cpp
@@ -297,7 +297,7 @@ mp3Decoder::DecodeNextChunk()
 }
 
 bool
-mp3Decoder::IsValidStream(uint8 *buffer, int size)
+mp3Decoder::IsValidStream(const uint8 *buffer, int size)
 {
 	// check 3 consecutive frame headers to make sure
 	// that the length encoded in the header is correct,
@@ -325,9 +325,9 @@ mp3Decoder::IsValidStream(uint8 *buffer, int size)
 }
 
 int
-mp3Decoder::GetFrameLength(void *header)
+mp3Decoder::GetFrameLength(const void *header)
 {
-	uint8 *h = (uint8 *)header;
+	const uint8 *h = static_cast<const uint8 *>(header);
 
 	if (h[0] != 0xff)
 		return -1;
diff --git a/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.h b/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.h
index 3537d3580e..59bdd74d52 100644
--- a/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.h
+++ b/src/add-ons/media/plugins/mp3_decoder/mp3DecoderPlugin.h
@@ -51,8 +51,8 @@ public:
 					   
 private:
 	status_t	DecodeNextChunk();
-	bool		IsValidStream(uint8 *buffer, int size);
-	int			GetFrameLength(void *header);	
+	bool		IsValidStream(const uint8 *buffer, int size);
+	int			GetFrameLength(const void *header);	
 	
 private:
 	struct mpstr	fMpgLibPrivate;