diff --git a/sp/src/game/server/entitylist.cpp b/sp/src/game/server/entitylist.cpp
index 55d5614b..29d87f50 100644
--- a/sp/src/game/server/entitylist.cpp
+++ b/sp/src/game/server/entitylist.cpp
@@ -736,6 +736,12 @@ CBaseEntity *CGlobalEntityList::FindEntityCustomProcedural( CBaseEntity *pStartE
 
 			g_pScriptVM->ExecuteFunction( g_CustomProcedurals[i].hFunc, args, 5, &functionReturn, NULL, true );
 
+			if (pStartEntity && ToEnt( functionReturn.m_hScript ) == pStartEntity)
+			{
+				Warning( "WARNING: Custom procedural %s returned entity identical to start entity (%s), returning null\n", g_CustomProcedurals[i].szName, pStartEntity->GetDebugName() );
+				return NULL;
+			}
+
 			return ToEnt( functionReturn.m_hScript );
 		}
 	}