diff --git a/src/p_glnodes.cpp b/src/p_glnodes.cpp
index 1b34e8bbc..547cecace 100644
--- a/src/p_glnodes.cpp
+++ b/src/p_glnodes.cpp
@@ -338,7 +338,14 @@ static bool LoadGLSegs(FileReader * lump)
 					
 					ml->side=LittleShort(ml->side);
 					segs[i].sidedef = ldef->sidedef[ml->side];
-					segs[i].frontsector = ldef->sidedef[ml->side]->sector;
+					if (ldef->sidedef[ml->side] != NULL)
+					{
+						segs[i].frontsector = ldef->sidedef[ml->side]->sector;
+					}
+					else
+					{
+						segs[i].frontsector = NULL;
+					}
 					if (ldef->flags & ML_TWOSIDED && ldef->sidedef[ml->side^1] != NULL)
 					{
 						segs[i].backsector = ldef->sidedef[ml->side^1]->sector;
@@ -346,7 +353,7 @@ static bool LoadGLSegs(FileReader * lump)
 					else
 					{
 						ldef->flags &= ~ML_TWOSIDED;
-						segs[i].backsector = 0;
+						segs[i].backsector = NULL;
 					}
 	
 				}
@@ -385,7 +392,14 @@ static bool LoadGLSegs(FileReader * lump)
 					
 					ml->side=LittleShort(ml->side);
 					segs[i].sidedef = ldef->sidedef[ml->side];
-					segs[i].frontsector = ldef->sidedef[ml->side]->sector;
+					if (ldef->sidedef[ml->side] != NULL)
+					{
+						segs[i].frontsector = ldef->sidedef[ml->side]->sector;
+					}
+					else
+					{
+						segs[i].frontsector = NULL;
+					}
 					if (ldef->flags & ML_TWOSIDED && ldef->sidedef[ml->side^1] != NULL)
 					{
 						segs[i].backsector = ldef->sidedef[ml->side^1]->sector;
@@ -393,7 +407,7 @@ static bool LoadGLSegs(FileReader * lump)
 					else
 					{
 						ldef->flags &= ~ML_TWOSIDED;
-						segs[i].backsector = 0;
+						segs[i].backsector = NULL;
 					}
 	
 				}