diff --git a/src/coreclr/vm/crst.cpp b/src/coreclr/vm/crst.cpp
index 76139417c32d77..647d9f4f4e9979 100644
--- a/src/coreclr/vm/crst.cpp
+++ b/src/coreclr/vm/crst.cpp
@@ -24,6 +24,10 @@
 #ifndef DACCESS_COMPILE
 Volatile<LONG> g_ShutdownCrstUsageCount = 0;
 
+#ifdef _DEBUG
+thread_local int t_unsafeAnyModeHeldCount = 0;
+#endif
+
 //-----------------------------------------------------------------
 // Initialize critical section
 //-----------------------------------------------------------------
@@ -220,6 +224,18 @@ void CrstBase::Enter(INDEBUG(NoLevelCheckFlag noLevelCheckFlag/* = CRST_LEVEL_CH
 
     _ASSERTE(IsCrstInitialized());
 
+#ifdef _DEBUG
+    // Detect attempts to take a default (GC_TRIGGERS) lock while holding a CRST_UNSAFE_ANYMODE lock.
+    // Taking a default lock can trigger a GC, which is illegal while a CRST_UNSAFE_ANYMODE lock is held.
+    if (!(m_dwFlags & (CRST_UNSAFE_ANYMODE | CRST_UNSAFE_COOPGC | CRST_GC_NOTRIGGER_WHEN_TAKEN)))
+    {
+        _ASSERTE_MSG(t_unsafeAnyModeHeldCount == 0,
+            "Taking a CRST_DEFAULT lock while a CRST_UNSAFE_ANYMODE lock or "
+            "SimpleRWLock COOPERATIVE_OR_PREEMPTIVE lock is held is illegal. "
+            "The default lock may trigger a GC, which is not allowed under ANYMODE locks.");
+    }
+#endif
+
     BOOL fIsCriticalSectionEnteredAfterFailingOnce = FALSE;
 
     Thread * pThread;
@@ -260,6 +276,11 @@ void CrstBase::Enter(INDEBUG(NoLevelCheckFlag noLevelCheckFlag/* = CRST_LEVEL_CH
 
 #ifdef _DEBUG
     PostEnter();
+
+    if (m_dwFlags & CRST_UNSAFE_ANYMODE)
+    {
+        t_unsafeAnyModeHeldCount++;
+    }
 #endif
 
     if (fToggle)
@@ -280,6 +301,11 @@ void CrstBase::Leave()
     _ASSERTE(IsCrstInitialized());
 
 #ifdef _DEBUG
+    if (m_dwFlags & CRST_UNSAFE_ANYMODE)
+    {
+        t_unsafeAnyModeHeldCount--;
+    }
+
     PreLeave ();
 #endif //_DEBUG
 
diff --git a/src/coreclr/vm/crst.h b/src/coreclr/vm/crst.h
index fe499fd365b298..280c575aaa8352 100644
--- a/src/coreclr/vm/crst.h
+++ b/src/coreclr/vm/crst.h
@@ -95,6 +95,12 @@
 // Total count of Crst lock  of the type (Shutdown) that are currently in use
 extern Volatile<LONG> g_ShutdownCrstUsageCount;
 
+#ifdef _DEBUG
+// Per-thread count of CRST_UNSAFE_ANYMODE (and equivalent) locks currently held.
+// Used to detect illegal acquisition of GC_TRIGGERS locks under ANYMODE locks.
+extern thread_local int t_unsafeAnyModeHeldCount;
+#endif
+
 // The CRST.
 class CrstBase
 {
diff --git a/src/coreclr/vm/simplerwlock.cpp b/src/coreclr/vm/simplerwlock.cpp
index dfe54a987f10bf..f63cd6d9236217 100644
--- a/src/coreclr/vm/simplerwlock.cpp
+++ b/src/coreclr/vm/simplerwlock.cpp
@@ -44,6 +44,16 @@ void SimpleRWLock::EnterRead()
     CheckGCNoTrigger();
 #endif //ENABLE_CONTRACTS_IMPL
 
+#ifdef _DEBUG
+    if (m_gcMode == PREEMPTIVE)
+    {
+        _ASSERTE_MSG(t_unsafeAnyModeHeldCount == 0,
+            "Taking a PREEMPTIVE SimpleRWLock while a COOPERATIVE_OR_PREEMPTIVE lock or "
+            "CRST_UNSAFE_ANYMODE lock is held is illegal. "
+            "The PREEMPTIVE lock may trigger a GC, which is not allowed under ANYMODE locks.");
+    }
+#endif
+
     GCX_MAYBE_PREEMP(m_gcMode == PREEMPTIVE);
 
 #ifdef _DEBUG
@@ -135,6 +145,16 @@ void SimpleRWLock::EnterWrite()
     CheckGCNoTrigger();
 #endif //ENABLE_CONTRACTS_IMPL
 
+#ifdef _DEBUG
+    if (m_gcMode == PREEMPTIVE)
+    {
+        _ASSERTE_MSG(t_unsafeAnyModeHeldCount == 0,
+            "Taking a PREEMPTIVE SimpleRWLock while a COOPERATIVE_OR_PREEMPTIVE lock or "
+            "CRST_UNSAFE_ANYMODE lock is held is illegal. "
+            "The PREEMPTIVE lock may trigger a GC, which is not allowed under ANYMODE locks.");
+    }
+#endif
+
     GCX_MAYBE_PREEMP(m_gcMode == PREEMPTIVE);
 
 #ifdef _DEBUG
@@ -267,6 +287,11 @@ void SimpleRWLock::PostEnter()
             INCONTRACT(pThread->BeginNoTriggerGC(__FILE__, __LINE__));
         }
     }
+
+    if (m_gcMode == COOPERATIVE_OR_PREEMPTIVE)
+    {
+        t_unsafeAnyModeHeldCount++;
+    }
 }
 
 //=====================================================================
@@ -276,6 +301,11 @@ void SimpleRWLock::PreLeave()
 {
     WRAPPER_NO_CONTRACT;
 
+    if (m_gcMode == COOPERATIVE_OR_PREEMPTIVE)
+    {
+        t_unsafeAnyModeHeldCount--;
+    }
+
     if (m_countNoTriggerGC > 0)
     {
         DWORD countNoTriggerGC = InterlockedDecrement(&m_countNoTriggerGC);
diff --git a/src/coreclr/vm/simplerwlock.hpp b/src/coreclr/vm/simplerwlock.hpp
index d8b90515a817a0..71780ddce8b30f 100644
--- a/src/coreclr/vm/simplerwlock.hpp
+++ b/src/coreclr/vm/simplerwlock.hpp
@@ -9,6 +9,10 @@
 
 #include "threads.h"
 
+#ifdef _DEBUG
+extern thread_local int t_unsafeAnyModeHeldCount;
+#endif
+
 class SimpleRWLock;
 
 //-------------------------------------------------------------------------------------------