diff --git a/renderdoc/os/os_specific.h b/renderdoc/os/os_specific.h
index ce4796980..b70feae00 100644
--- a/renderdoc/os/os_specific.h
+++ b/renderdoc/os/os_specific.h
@@ -204,6 +204,7 @@ int32_t Dec32(volatile int32_t *i);
 int64_t Inc64(volatile int64_t *i);
 int64_t Dec64(volatile int64_t *i);
 int64_t ExchAdd64(volatile int64_t *i, int64_t a);
+int32_t CmpExch32(volatile int32_t *dest, int32_t exch, int32_t comp);
 };
 
 namespace Callstack
diff --git a/renderdoc/os/posix/posix_threading.cpp b/renderdoc/os/posix/posix_threading.cpp
index 08a7ab1d8..bc915391b 100644
--- a/renderdoc/os/posix/posix_threading.cpp
+++ b/renderdoc/os/posix/posix_threading.cpp
@@ -59,6 +59,11 @@ int64_t ExchAdd64(volatile int64_t *i, int64_t a)
 {
   return __sync_add_and_fetch(i, int64_t(a));
 }
+
+int32_t CmpExch32(volatile int32_t *dest, int32_t exch, int32_t comp)
+{
+  return __sync_val_compare_and_swap(dest, comp, exch);
+}
 };
 
 namespace Threading
diff --git a/renderdoc/os/win32/win32_threading.cpp b/renderdoc/os/win32/win32_threading.cpp
index 5c86723ae..946be7192 100644
--- a/renderdoc/os/win32/win32_threading.cpp
+++ b/renderdoc/os/win32/win32_threading.cpp
@@ -72,6 +72,11 @@ int64_t ExchAdd64(volatile int64_t *i, int64_t a)
 {
   return (int64_t)InterlockedExchangeAdd64((volatile LONG64 *)i, a);
 }
+
+int32_t CmpExch32(volatile int32_t *dest, int32_t exch, int32_t comp)
+{
+  return (int32_t)InterlockedCompareExchange((volatile LONG *)dest, exch, comp);
+}
 };
 
 namespace Threading