diff --git a/src/g_level.cpp b/src/g_level.cpp
index 7a166dbc4..c031c6195 100644
--- a/src/g_level.cpp
+++ b/src/g_level.cpp
@@ -2029,9 +2029,9 @@ int IsPointInMap(double x, double y, double z)
 
 	for (uint32_t i = 0; i < subsector->numlines; i++)
 	{
-		// Skip single sided lines.
+		// Skip double sided lines.
 		seg_t *seg = subsector->firstline + i;
-		if (seg->backsector != nullptr)	continue;
+		if (seg->backsector != nullptr || seg->linedef == nullptr) continue;
 
 		divline_t dline;
 		P_MakeDivline(seg->linedef, &dline);