diff --git a/src/mesa/drivers/dri/i965/brw_draw.c b/src/mesa/drivers/dri/i965/brw_draw.c
index a7164dbf7d8..b91597a9f5d 100644
--- a/src/mesa/drivers/dri/i965/brw_draw.c
+++ b/src/mesa/drivers/dri/i965/brw_draw.c
@@ -92,8 +92,10 @@ get_hw_prim_for_gl_prim(int mode)
 {
    if (mode >= BRW_PRIM_OFFSET)
       return mode - BRW_PRIM_OFFSET;
-   else
+   else {
+      assert(mode < ARRAY_SIZE(prim_to_hw_prim));
       return prim_to_hw_prim[mode];
+   }
 }