diff --git a/src/serverenvironment.cpp b/src/serverenvironment.cpp
index 26b0dd1fa05f..d8972d04554a 100644
--- a/src/serverenvironment.cpp
+++ b/src/serverenvironment.cpp
@@ -394,19 +394,23 @@ void ActiveBlockList::update(std::vector<PlayerSAO*> &active_players,
 			std::inserter(blocks_removed, blocks_removed.end()));
 
 	/*
-		Some sanity checks
-	 */
+		Do some least-effort sanity checks to hopefully catch code bugs.
+	*/
 	assert(newlist.size() >= extralist.size());
 	assert(blocks_removed.size() <= m_list.size());
-	if (!blocks_added.empty())
-	  assert(newlist.count(*blocks_added.begin()) > 0);
+	if (!blocks_added.empty()) {
+		assert(newlist.count(*blocks_added.begin()) > 0);
+		assert(blocks_removed.count(*blocks_added.begin()) == 0);
+	}
 	if (!extra_blocks_added.empty()) {
-	  assert(newlist.count(*extra_blocks_added.begin()) > 0);
-	  assert(blocks_added.count(*extra_blocks_added.begin()) == 0);
+		assert(newlist.count(*extra_blocks_added.begin()) > 0);
+		assert(extralist.count(*extra_blocks_added.begin()) > 0);
+		assert(blocks_added.count(*extra_blocks_added.begin()) == 0);
 	}
 	if (!blocks_removed.empty()) {
-	  assert(newlist.count(*blocks_removed.begin()) == 0);
-	  assert(m_list.count(*blocks_removed.begin()) > 0);
+		assert(newlist.count(*blocks_removed.begin()) == 0);
+		assert(extralist.count(*blocks_removed.begin()) == 0);
+		assert(m_list.count(*blocks_removed.begin()) > 0);
 	}
 
 	/*