diff --git a/stepmania/src/RageThreads.cpp b/stepmania/src/RageThreads.cpp
index c98e3760a9..bc8211f195 100644
--- a/stepmania/src/RageThreads.cpp
+++ b/stepmania/src/RageThreads.cpp
@@ -13,6 +13,9 @@
 #include "stdafx.h"
 
 #include "RageThreads.h"
+#include "RageTimer.h"
+#include "RageLog.h"
+#include "RageUtil.h"
 
 RageMutex::RageMutex()
 {
@@ -69,6 +72,27 @@ void RageMutex::Unlock()
 	SDL_UnlockMutex(mut);
 }
 
+LockMutex::LockMutex(RageMutex &mut, const char *file_, int line_): 
+	mutex(mut),
+	file(file_),
+	line(line_),
+	locked_at(RageTimer::GetTimeSinceStart())
+{
+	mutex.Lock();
+}
+
+LockMutex::~LockMutex()
+{
+	mutex.Unlock();
+
+	if(file)
+	{
+		float dur = RageTimer::GetTimeSinceStart() - locked_at;
+		if(dur > 0.015)
+			LOG->Trace(ssprintf("Lock at %s:%i took %f", file, line, dur));
+	}
+}
+
 /*
 -----------------------------------------------------------------------------
  File: RageThreads
diff --git a/stepmania/src/RageThreads.h b/stepmania/src/RageThreads.h
index 3f3fd42232..eb14785c41 100644
--- a/stepmania/src/RageThreads.h
+++ b/stepmania/src/RageThreads.h
@@ -27,10 +27,31 @@ class LockMutex
 {
 	RageMutex &mutex;
 
+	const char *file;
+	int line;
+	float locked_at;
+
 public:
-	LockMutex(RageMutex &mut): mutex(mut) { mutex.Lock(); }
-	~LockMutex() { mutex.Unlock(); }
-	LockMutex(LockMutex &cpy): mutex(cpy.mutex) { mutex.Lock(); }
+	LockMutex(RageMutex &mut, const char *file, int line);
+	LockMutex(RageMutex &mut): mutex(mut), file(NULL), line(-1), locked_at(0) { mutex.Lock(); }
+	~LockMutex();
+	LockMutex(LockMutex &cpy): mutex(cpy.mutex), file(cpy.file), line(cpy.line), locked_at(cpy.locked_at) { mutex.Lock(); }
 };
 
+/* Double-abstracting __LINE__ lets us append it to other text, to generate
+ * locally unique variable names.  (Otherwise we get "LocalLock__LINE__".) I'm
+ * not sure why this works, but it does, in both VC and GCC. */
+
+#ifdef DEBUG
+/* Use the debug version, which logs if something holds a lock for a long time.
+ * __FUNCTION__ is nonstandard, but both GCC and VC support it; VC doesn't
+ * support the standard, __func__. */
+#define LockMutL2(m, l) LockMutex LocalLock ## l (m, __FUNCTION__, __LINE__)
+#else
+#define LockMutL2(m, l) LockMutex LocalLock ## l (m)
+#endif
+
+#define LockMutL(m, l) LockMutL2(m, l)
+#define LockMut(m) LockMutL(m, __LINE__)
+
 #endif