PaperMC/nms-patches/ChunkGenerator.patch

--- a/net/minecraft/server/ChunkGenerator.java
+++ b/net/minecraft/server/ChunkGenerator.java
@@ -147,6 +147,18 @@
                 StructureStart structurestart1 = StructureStart.a;
                 BiomeBase biomebase = biomemanager.a(new BlockPosition(chunkcoordintpair.d() + 9, 0, chunkcoordintpair.e() + 9));
 
+                // CraftBukkit start
+                if (structuregenerator == WorldGenerator.STRONGHOLD) {
+                    synchronized (structuregenerator) {
+                        if (structuregenerator.a(biomemanager, chunkgenerator, seededrandom, chunkcoordintpair.x, chunkcoordintpair.z, biomebase)) {
+                            StructureStart structurestart2 = structuregenerator.a().create(structuregenerator, chunkcoordintpair.x, chunkcoordintpair.z, StructureBoundingBox.a(), i, chunkgenerator.getSeed());
+
+                            structurestart2.a(this, definedstructuremanager, chunkcoordintpair.x, chunkcoordintpair.z, biomebase);
+                            structurestart1 = structurestart2.e() ? structurestart2 : StructureStart.a;
+                        }
+                    }
+                } else
+                // CraftBukkit end
                 if (structuregenerator.a(biomemanager, chunkgenerator, seededrandom, chunkcoordintpair.x, chunkcoordintpair.z, biomebase)) {
                     StructureStart structurestart2 = structuregenerator.a().create(structuregenerator, chunkcoordintpair.x, chunkcoordintpair.z, StructureBoundingBox.a(), i, chunkgenerator.getSeed());