diff --git a/GL/draw.c b/GL/draw.c
index 07dd976..d54e775 100644
--- a/GL/draw.c
+++ b/GL/draw.c
@@ -509,7 +509,7 @@ static Vertex* draw_line(Vertex* dst, Vertex* v1, Vertex* v2) {
     float dx = ov2.xyz[0] - ov1.xyz[0];
     float dy = ov2.xyz[1] - ov1.xyz[1];
 
-    float inverse_mag = frsqrt((dx*dx) + (dy*dy)) * HALF_LINE_WIDTH;
+    float inverse_mag = fast_rsqrt((dx*dx) + (dy*dy)) * HALF_LINE_WIDTH;
     float nx = -dy * inverse_mag;
     float ny =  dx * inverse_mag;
 
diff --git a/GL/private.h b/GL/private.h
index 266af80..8230f01 100644
--- a/GL/private.h
+++ b/GL/private.h
@@ -260,6 +260,12 @@ do {                 \
     memcpy_vertex(b, &c); \
 } while(0)
 
+#ifdef __DREAMCAST__
+#define fast_rsqrt(x) frsqrt(x)
+#else
+#define fast_rsqrt(x) (1.0f / __builtin_sqrtf(x))
+#endif
+
 /* ClipVertex doesn't have room for these, so we need to parse them
  * out separately. Potentially 'w' will be housed here if we support oargb */
 typedef struct {