diff --git a/Source/codec.cpp b/Source/codec.cpp
index 49a7831d8..d8019fd8f 100644
--- a/Source/codec.cpp
+++ b/Source/codec.cpp
@@ -19,7 +19,7 @@ typedef struct CodecSignature {
 
 #define BLOCKSIZE 64
 
-int codec_decode(BYTE *pbSrcDst, DWORD size, char *pszPassword)
+int codec_decode(BYTE *pbSrcDst, DWORD size, const char *pszPassword)
 {
 	char buf[128];
 	char dst[SHA1HashSize];
@@ -102,7 +102,7 @@ DWORD codec_get_encoded_len(DWORD dwSrcBytes)
 	return dwSrcBytes + sizeof(CodecSignature);
 }
 
-void codec_encode(BYTE *pbSrcDst, DWORD size, int size_64, char *pszPassword)
+void codec_encode(BYTE *pbSrcDst, DWORD size, int size_64, const char *pszPassword)
 {
 	char buf[128];
 	char tmp[SHA1HashSize];
diff --git a/Source/codec.h b/Source/codec.h
index caf929337..859e366d1 100644
--- a/Source/codec.h
+++ b/Source/codec.h
@@ -12,10 +12,10 @@ DEVILUTION_BEGIN_NAMESPACE
 extern "C" {
 #endif
 
-int codec_decode(BYTE *pbSrcDst, DWORD size, char *pszPassword);
+int codec_decode(BYTE *pbSrcDst, DWORD size, const  char *pszPassword);
 void codec_init_key(int unused, char *pszPassword);
 DWORD codec_get_encoded_len(DWORD dwSrcBytes);
-void codec_encode(BYTE *pbSrcDst, DWORD size, int size_64, char *pszPassword);
+void codec_encode(BYTE *pbSrcDst, DWORD size, int size_64, const char *pszPassword);
 
 #ifdef __cplusplus
 }