diff --git a/ircd/db.cc b/ircd/db.cc
index eabe4d0e9..a39f4ec32 100644
--- a/ircd/db.cc
+++ b/ircd/db.cc
@@ -3190,6 +3190,13 @@ noexcept
 // Mutex
 //
 
+static_assert
+(
+	sizeof(rocksdb::port::Mutex) <= sizeof(pthread_mutex_t) + 1,
+	"link-time punning of our structure won't work if the structure is larger "
+	"than the one rocksdb has assumed space for."
+);
+
 rocksdb::port::Mutex::Mutex()
 {
 	#ifdef RB_DEBUG_DB_PORT_
@@ -3267,6 +3274,13 @@ rocksdb::port::Mutex::AssertHeld()
 // RWMutex
 //
 
+static_assert
+(
+	sizeof(rocksdb::port::RWMutex) <= sizeof(pthread_rwlock_t),
+	"link-time punning of our structure won't work if the structure is larger "
+	"than the one rocksdb has assumed space for."
+);
+
 rocksdb::port::RWMutex::RWMutex()
 {
 	#ifdef RB_DEBUG_DB_PORT_
@@ -3347,6 +3361,13 @@ rocksdb::port::RWMutex::WriteUnlock()
 // CondVar
 //
 
+static_assert
+(
+	sizeof(rocksdb::port::CondVar) <= sizeof(pthread_cond_t) + sizeof(void *),
+	"link-time punning of our structure won't work if the structure is larger "
+	"than the one rocksdb has assumed space for."
+);
+
 rocksdb::port::CondVar::CondVar(Mutex *mu)
 :mu{mu}
 {