diff --git a/src/GPU3D_Soft.cpp b/src/GPU3D_Soft.cpp
index 458a4877..90eac90f 100644
--- a/src/GPU3D_Soft.cpp
+++ b/src/GPU3D_Soft.cpp
@@ -567,7 +567,7 @@ void SoftRenderer::PlotTranslucentPixel(const GPU3D& gpu3d, u32 pixeladdr, u32 c
     AttrBuffer[pixeladdr] = attr;
 }
 
-void SoftRenderer::CheckForLine(RendererPolygon* rp)
+void SoftRenderer::CheckForLine(RendererPolygon* rp) const
 {
     Polygon* polygon = rp->PolyData;
 
diff --git a/src/GPU3D_Soft.h b/src/GPU3D_Soft.h
index 1c4d7735..23661580 100644
--- a/src/GPU3D_Soft.h
+++ b/src/GPU3D_Soft.h
@@ -457,7 +457,7 @@ private:
     void TextureLookup(const GPU& gpu, u32 texparam, u32 texpal, s16 s, s16 t, u16* color, u8* alpha) const;
     u32 RenderPixel(const GPU& gpu, const Polygon* polygon, u8 vr, u8 vg, u8 vb, s16 s, s16 t) const;
     void PlotTranslucentPixel(const GPU3D& gpu3d, u32 pixeladdr, u32 color, u32 z, u32 polyattr, u32 shadow);
-    void CheckForLine(RendererPolygon* rp);
+    void CheckForLine(RendererPolygon* rp) const;
     void SetupPolygonLeftEdge(RendererPolygon* rp, s32 y) const;
     void SetupPolygonRightEdge(RendererPolygon* rp, s32 y) const;
     void SetupPolygon(RendererPolygon* rp, Polygon* polygon) const;