diff --git a/src/acs/environment.cpp b/src/acs/environment.cpp
index 0a4939811..b14d825df 100644
--- a/src/acs/environment.cpp
+++ b/src/acs/environment.cpp
@@ -228,8 +228,7 @@ void Environment::loadModule(ACSVM::Module *module)
 	if (name->i == (size_t)LUMPERROR)
 	{
 		// No lump given for module.
-		CONS_Alert(CONS_WARNING, "Could not find ACS module \"%s\"; scripts will not function properly!\n", name->s->str);
-		return; //throw ACSVM::ReadError("file open failure");
+		throw ACSVM::ReadError("invalid lump");
 	}
 
 	lumpLen = W_LumpLength(name->i);
@@ -280,9 +279,7 @@ void Environment::loadModule(ACSVM::Module *module)
 	}
 	else
 	{
-		// Unlike Hexen, a BEHAVIOR lump is not required.
-		// Simply ignore in this instance.
-		CONS_Debug(DBG_SETUP, "ACS module has no data, ignoring...\n");
+		throw ACSVM::ReadError("file empty");
 	}
 }
 
diff --git a/src/acs/interface.cpp b/src/acs/interface.cpp
index 60689d24a..50eb51241 100644
--- a/src/acs/interface.cpp
+++ b/src/acs/interface.cpp
@@ -142,6 +142,13 @@ void ACS_LoadLevelScripts(size_t mapID)
 	map->active = true;
 
 	// Insert BEHAVIOR lump into the list.
+	virtres_t *vRes = vres_GetMap(mapheaderinfo[mapID]->lumpnum);
+	auto _ = srb2::finally([vRes]() { vres_Free(vRes); });
+
+	// Unlike Hexen, a BEHAVIOR lump is not required.
+	// Simply ignore in this instance.
+	virtlump_t *vLump = vres_Find(vRes, "BEHAVIOR");
+	if (vLump != nullptr && vLump->size > 0)
 	{
 		ACSVM::ModuleName name = ACSVM::ModuleName(
 			env->getString( mapheaderinfo[mapID]->lumpname ),
@@ -150,6 +157,7 @@ void ACS_LoadLevelScripts(size_t mapID)
 		);
 
 		modules.push_back(env->getModule(name));
+		CONS_Debug(DBG_SETUP, "Found BEHAVIOR lump.\n");
 	}
 
 	if (modules.empty() == false)