diff --git a/common/vid_glx.c b/common/vid_glx.c
index 2813800..9fc31e6 100644
--- a/common/vid_glx.c
+++ b/common/vid_glx.c
@@ -113,7 +113,7 @@ qboolean isPermedia = false;
 
 /*-----------------------------------------------------------------------*/
 void
-D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height)
+D_BeginDirectRect(int x, int y, const byte *pbitmap, int width, int height)
 {
 // direct drawing of the "accessing disk" icon isn't supported under GLX
 }
diff --git a/common/vid_null.c b/common/vid_null.c
index a8b816b..553c7b7 100644
--- a/common/vid_null.c
+++ b/common/vid_null.c
@@ -76,7 +76,7 @@ D_BeginDirectRect
 ================
 */
 void
-D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height)
+D_BeginDirectRect(int x, int y, const byte *pbitmap, int width, int height)
 {
 }
 
diff --git a/common/vid_sdl.c b/common/vid_sdl.c
index 744b538..b98fec6 100644
--- a/common/vid_sdl.c
+++ b/common/vid_sdl.c
@@ -1112,10 +1112,10 @@ VID_Update(vrect_t *rects)
 }
 
 void
-D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height)
+D_BeginDirectRect(int x, int y, const byte *pbitmap, int width, int height)
 {
     int err, i;
-    byte *src;
+    const byte *src;
     unsigned *dst;
     int pitch;
     SDL_Rect subrect;
diff --git a/common/vid_sgl.c b/common/vid_sgl.c
index 89f258c..fbe6d5b 100644
--- a/common/vid_sgl.c
+++ b/common/vid_sgl.c
@@ -58,7 +58,7 @@ qboolean gl_mtexable;
 cvar_t gl_ztrick = { "gl_ztrick", "1" };
 
 void VID_Update(vrect_t *rects) {}
-void D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height) {}
+void D_BeginDirectRect(int x, int y, const byte *pbitmap, int width, int height) {}
 void D_EndDirectRect(int x, int y, int width, int height) {}
 
 /*
diff --git a/common/vid_wgl.c b/common/vid_wgl.c
index 4ed3cf2..8c8efc6 100644
--- a/common/vid_wgl.c
+++ b/common/vid_wgl.c
@@ -217,7 +217,7 @@ VID_ForceUnlockedAndReturnState(void)
 }
 
 void
-D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height)
+D_BeginDirectRect(int x, int y, const byte *pbitmap, int width, int height)
 {
 }
 
diff --git a/common/vid_win.c b/common/vid_win.c
index 0e178a4..bad81ad 100644
--- a/common/vid_win.c
+++ b/common/vid_win.c
@@ -2266,7 +2266,7 @@ D_BeginDirectRect
 ================
 */
 void
-D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height)
+D_BeginDirectRect(int x, int y, const byte *pbitmap, int width, int height)
 {
     int i, j, reps, repshift;
     vrect_t rect;
diff --git a/common/vid_x.c b/common/vid_x.c
index 3e2349c..4b4f15d 100644
--- a/common/vid_x.c
+++ b/common/vid_x.c
@@ -1166,7 +1166,7 @@ Sys_SendKeyEvents(void)
 }
 
 void
-D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height)
+D_BeginDirectRect(int x, int y, const byte *pbitmap, int width, int height)
 {
 // direct drawing of the "accessing disk" icon isn't supported under Linux
 }
diff --git a/include/d_iface.h b/include/d_iface.h
index 7c72be2..f2d9754 100644
--- a/include/d_iface.h
+++ b/include/d_iface.h
@@ -152,7 +152,8 @@ extern vec3_t r_pright, r_pup, r_ppn;
 
 
 void D_Aff8Patch(void *pcolormap);
-void D_BeginDirectRect(int x, int y, byte *pbitmap, int width, int height);
+void D_BeginDirectRect(int x, int y, const byte *pbitmap, int width,
+		       int height);
 void D_DisableBackBufferAccess(void);
 void D_EndDirectRect(int x, int y, int width, int height);
 void D_PolysetDraw(void);