diff --git a/qbsp/brush.c b/qbsp/brush.c
index 6f7777f2..1152081c 100644
--- a/qbsp/brush.c
+++ b/qbsp/brush.c
@@ -237,7 +237,7 @@ PlaneHash_Init(void)
  * - Returns a global plane number and the side that will be the front
  */
 static int
-NewPlane(vec3_t normal, vec_t dist, int *side)
+NewPlane(const vec3_t normal, const vec_t dist, int *side)
 {
     plane_t *plane;
     vec_t len;
@@ -262,10 +262,10 @@ NewPlane(vec3_t normal, vec_t dist, int *side)
  * - Returns a global plane number and the side that will be the front
  */
 int
-FindPlane(plane_t *plane, int *side)
+FindPlane(const plane_t *plane, int *side)
 {
     const int bins[] = { 0, 1, -1 };
-    plane_t *p;
+    const plane_t *p;
     int hash, h;
     int i;
 
diff --git a/qbsp/qbsp.h b/qbsp/qbsp.h
index 4d3f917a..7510ddf4 100644
--- a/qbsp/qbsp.h
+++ b/qbsp/qbsp.h
@@ -431,7 +431,7 @@ typedef struct brush_s {
 void FreeBrushsetBrushes(brush_t *pBrushList);
 
 void PlaneHash_Init(void);
-int FindPlane(plane_t *dplane, int *side);
+int FindPlane(const plane_t *plane, int *side);
 
 //=============================================================================