diff --git a/src/m_misc.c b/src/m_misc.c
index 17f08f87..27a31099 100644
--- a/src/m_misc.c
+++ b/src/m_misc.c
@@ -178,7 +178,7 @@ long M_FileLength(FILE *handle)
 // M_WriteFile
 //
 
-boolean M_WriteFile(const char *name, void *source, int length)
+boolean M_WriteFile(const char *name, const void *source, int length)
 {
     FILE *handle;
     int	count;
diff --git a/src/m_misc.h b/src/m_misc.h
index 81b767fe..90855d18 100644
--- a/src/m_misc.h
+++ b/src/m_misc.h
@@ -25,7 +25,7 @@
 
 #include "doomtype.h"
 
-boolean M_WriteFile(const char *name, void *source, int length);
+boolean M_WriteFile(const char *name, const void *source, int length);
 int M_ReadFile(const char *name, byte **buffer);
 void M_MakeDirectory(const char *dir);
 char *M_TempFile(const char *s);