diff --git a/renderdoc/core/resource_manager.cpp b/renderdoc/core/resource_manager.cpp
index ef1482f62..77674c387 100644
--- a/renderdoc/core/resource_manager.cpp
+++ b/renderdoc/core/resource_manager.cpp
@@ -125,6 +125,14 @@ FrameRefType ComposeFrameRefsDisjoint(FrameRefType x, FrameRefType y)
     return RDCMAX(x, y);
 }
 
+FrameRefType ComposeFrameRefsFirstKnown(FrameRefType first, FrameRefType second)
+{
+  if(eFrameRef_Minimum <= first && first <= eFrameRef_Maximum)
+    return first;
+  else
+    return second;
+}
+
 bool IncludesRead(FrameRefType refType)
 {
   switch(refType)
diff --git a/renderdoc/core/resource_manager.h b/renderdoc/core/resource_manager.h
index 663600746..370d23255 100644
--- a/renderdoc/core/resource_manager.h
+++ b/renderdoc/core/resource_manager.h
@@ -103,6 +103,11 @@ enum FrameRefType
   // read could, incorrectly, be observed. This is because read-only resources
   // are not reset, so the write from the previous replay may still be present.
   eFrameRef_WriteBeforeRead = 5,
+
+  // No reference info is available;
+  // This should only appear durring replay, and any (sub)resource with `Unknown`
+  // reference type should be conservatively reset before each replay.
+  eFrameRef_Unknown = 1000000000,
 };
 
 bool IncludesRead(FrameRefType refType);
@@ -135,6 +140,9 @@ FrameRefType ComposeFrameRefsUnordered(FrameRefType first, FrameRefType second);
 // frame refs of their subresources.
 FrameRefType ComposeFrameRefsDisjoint(FrameRefType x, FrameRefType y);
 
+// Returns whichever of `first` or `second` is valid.
+FrameRefType ComposeFrameRefsFirstKnown(FrameRefType first, FrameRefType second);
+
 bool IsDirtyFrameRef(FrameRefType refType);
 
 // Captures the possible initialization/reset requirements for resources.
@@ -200,6 +208,8 @@ enum InitPolicy
 // Return the initialization/reset requirements for a FrameRefType
 inline InitReqType InitReq(FrameRefType refType, InitPolicy policy, bool initialized)
 {
+  if(eFrameRef_Minimum > refType || refType > eFrameRef_Maximum)
+    return eInitReq_Copy;
 #define COPY_ONCE (initialized ? eInitReq_None : eInitReq_Copy)
 #define CLEAR_ONCE (initialized ? eInitReq_None : eInitReq_Clear)
   switch(policy)