diff --git a/Source/sweep.c b/Source/sweep.c
index a8d8971..112f1ef 100755
--- a/Source/sweep.c
+++ b/Source/sweep.c
@@ -1121,10 +1121,12 @@ static void InitEdgeDict( TESStesselator *tess )
 	w = (tess->bmax[0] - tess->bmin[0]);
 	h = (tess->bmax[1] - tess->bmin[1]);
 
-	smin = tess->bmin[0] - w - 0.01;
-	smax = tess->bmax[0] + w + 0.01;
-	tmin = tess->bmin[1] - h - 0.01;
-	tmax = tess->bmax[1] + h + 0.01;
+        /* If the bbox is empty, ensure that sentinels are not coincident by
+           slightly enlarging it. */
+	smin = tess->bmin[0] - (w > 0 ? w : 0.01);
+        smax = tess->bmax[0] + (w > 0 ? w : 0.01);
+        tmin = tess->bmin[1] - (h > 0 ? h : 0.01);
+        tmax = tess->bmax[1] + (h > 0 ? h : 0.01);
 
 	AddSentinel( tess, smin, smax, tmin );
 	AddSentinel( tess, smin, smax, tmax );