diff --git a/src/sync.cpp b/src/sync.cpp
index 87024ccdf..4ef419cd0 100644
--- a/src/sync.cpp
+++ b/src/sync.cpp
@@ -155,6 +155,16 @@ void AssertLockHeldInternal(const char* pszName, const char* pszFile, int nLine,
     abort();
 }
 
+void AssertLockNotHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs)
+{
+    for (const std::pair<void*, CLockLocation>& i : *lockstack) {
+        if (i.first == cs) {
+            fprintf(stderr, "Assertion failed: lock %s held in %s:%i; locks held:\n%s", pszName, pszFile, nLine, LocksHeld().c_str());
+            abort();
+        }
+    }
+}
+
 void DeleteLock(void* cs)
 {
     if (!lockdata.available) {
diff --git a/src/sync.h b/src/sync.h
index 0871c5fb4..2790fc6f2 100644
--- a/src/sync.h
+++ b/src/sync.h
@@ -75,14 +75,17 @@ void EnterCritical(const char* pszName, const char* pszFile, int nLine, void* cs
 void LeaveCritical();
 std::string LocksHeld();
 void AssertLockHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs);
+void AssertLockNotHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs);
 void DeleteLock(void* cs);
 #else
 void static inline EnterCritical(const char* pszName, const char* pszFile, int nLine, void* cs, bool fTry = false) {}
 void static inline LeaveCritical() {}
 void static inline AssertLockHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs) {}
+void static inline AssertLockNotHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs) {}
 void static inline DeleteLock(void* cs) {}
 #endif
 #define AssertLockHeld(cs) AssertLockHeldInternal(#cs, __FILE__, __LINE__, &cs)
+#define AssertLockNotHeld(cs) AssertLockNotHeldInternal(#cs, __FILE__, __LINE__, &cs)
 
 /**
  * Wrapped boost mutex: supports recursive locking, but no waiting