diff --git a/renderdoc/driver/d3d12/d3d12_dxil_debug.cpp b/renderdoc/driver/d3d12/d3d12_dxil_debug.cpp
index 45709b406..5f3eba460 100644
--- a/renderdoc/driver/d3d12/d3d12_dxil_debug.cpp
+++ b/renderdoc/driver/d3d12/d3d12_dxil_debug.cpp
@@ -995,7 +995,7 @@ void D3D12APIWrapper::AddCBufferToGlobalState(const BindingSlot &slot, bytebuf &
       RDCASSERTMSG("Reassigning previously filled cbuffer", targetVars.empty());
 
       ConstantBlockReference constantBlockRef = {i, arrayIndex};
-      m_ConstantBlocksDatas[constantBlockRef] = cbufData;
+      m_ConstantBlocksDatas[constantBlockRef] = {cbufData, cb.byteSize};
       rdcstr resName = Debugger::GetResourceReferenceName(m_Program, ResourceClass::CBuffer, slot);
       m_ConstantBlocks[i].name = resName;
 
diff --git a/renderdoc/driver/d3d12/d3d12_dxil_debug.h b/renderdoc/driver/d3d12/d3d12_dxil_debug.h
index 773f2481f..9cae66f45 100644
--- a/renderdoc/driver/d3d12/d3d12_dxil_debug.h
+++ b/renderdoc/driver/d3d12/d3d12_dxil_debug.h
@@ -113,7 +113,7 @@ public:
     return m_WorkgroupProperties;
   }
   const rdcarray<ShaderVariable> &GetConstantBlocks() const override { return m_ConstantBlocks; }
-  const std::map<ConstantBlockReference, bytebuf> &GetConstantBlocksDatas() const override
+  const std::map<ConstantBlockReference, ConstantBlockData> &GetConstantBlocksDatas() const override
   {
     return m_ConstantBlocksDatas;
   }
@@ -160,7 +160,7 @@ private:
   rdcarray<rdcflatmap<ShaderBuiltin, ShaderVariable>> m_ThreadsBuiltins;
   rdcarray<SourceVariableMapping> m_SourceVars;
   rdcarray<ShaderVariable> m_ConstantBlocks;
-  std::map<ConstantBlockReference, bytebuf> m_ConstantBlocksDatas;
+  std::map<ConstantBlockReference, ConstantBlockData> m_ConstantBlocksDatas;
   ShaderVariable m_InputPlaceholder;
   uint32_t m_SubgroupSize = 1;
 
diff --git a/renderdoc/driver/shaders/dxil/dxil_debug.cpp b/renderdoc/driver/shaders/dxil/dxil_debug.cpp
index 0a975d7ae..b092c92c5 100644
--- a/renderdoc/driver/shaders/dxil/dxil_debug.cpp
+++ b/renderdoc/driver/shaders/dxil/dxil_debug.cpp
@@ -2595,7 +2595,7 @@ bool ThreadState::ExecuteInstruction(const rdcarray<ThreadState> &workgroup)
                   auto it = m_GlobalState.constantBlocksDatas.find(constantBlockRef);
                   if(it != m_GlobalState.constantBlocksDatas.end())
                   {
-                    const bytebuf &cbufferData = it->second;
+                    const bytebuf &cbufferData = it->second.bufferData;
                     if(cbufferData.size() != 0)
                     {
                       size_t offset = 0;
@@ -2681,9 +2681,9 @@ bool ThreadState::ExecuteInstruction(const rdcarray<ThreadState> &workgroup)
                 auto it = m_GlobalState.constantBlocksDatas.find(constantBlockRef);
                 if(it != m_GlobalState.constantBlocksDatas.end())
                 {
-                  const bytebuf &cbufferData = it->second;
-                  const uint32_t bufferSize = (uint32_t)cbufferData.size();
-                  const uint32_t maxIndex = AlignUp16(bufferSize) / 16;
+                  const bytebuf &cbufferData = it->second.bufferData;
+                  const uint32_t dataSize = (uint32_t)(it->second.byteSize);
+                  const uint32_t maxIndex = AlignUp16(dataSize) / 16;
                   RDCASSERTMSG("Out of bounds cbuffer load", regIndex < maxIndex, regIndex, maxIndex);
                   if(regIndex < maxIndex)
                   {
@@ -2691,7 +2691,7 @@ bool ThreadState::ExecuteInstruction(const rdcarray<ThreadState> &workgroup)
                     const uint32_t byteWidth = 4;
                     const byte *base = cbufferData.data() + dataOffset;
                     const uint32_t *data = (const uint32_t *)base;
-                    const uint32_t numComps = RDCMIN(4U, (bufferSize - dataOffset) / byteWidth);
+                    const uint32_t numComps = RDCMIN(4U, (dataSize - dataOffset) / byteWidth);
                     for(uint32_t c = 0; c < numComps; c++)
                       result.value.u32v[c] = data[c];
                   }
diff --git a/renderdoc/driver/shaders/dxil/dxil_debug.h b/renderdoc/driver/shaders/dxil/dxil_debug.h
index 07ee9158e..fb8b56671 100644
--- a/renderdoc/driver/shaders/dxil/dxil_debug.h
+++ b/renderdoc/driver/shaders/dxil/dxil_debug.h
@@ -263,6 +263,12 @@ struct SRVInfo
   ResourceInfo resInfo;
 };
 
+struct ConstantBlockData
+{
+  bytebuf bufferData;
+  size_t byteSize;
+};
+
 enum class ThreadProperty : uint32_t
 {
   Helper,
@@ -346,7 +352,7 @@ public:
   virtual const ShaderVariable &GetInputPlaceholder() const = 0;
   virtual const rdcarray<DXILDebug::ThreadProperties> &GetWorkgroupProperties() const = 0;
   virtual const rdcarray<ShaderVariable> &GetConstantBlocks() const = 0;
-  virtual const std::map<ConstantBlockReference, bytebuf> &GetConstantBlocksDatas() const = 0;
+  virtual const std::map<ConstantBlockReference, ConstantBlockData> &GetConstantBlocksDatas() const = 0;
   virtual const BuiltinInputs &GetBuiltins() const = 0;
   virtual uint32_t GetSubgroupSize() const = 0;
   virtual const rdcarray<rdcflatmap<ShaderBuiltin, ShaderVariable>> &GetThreadsBuiltins() const = 0;
@@ -795,7 +801,7 @@ struct GlobalState
 
   // allocated storage for opaque uniform blocks, does not change over the course of debugging
   rdcarray<ShaderVariable> constantBlocks;
-  std::map<ConstantBlockReference, bytebuf> constantBlocksDatas;
+  std::map<ConstantBlockReference, ConstantBlockData> constantBlocksDatas;
 
   rdcarray<Id> groupSharedMemoryIds;
   // resources may be read-write but the variable itself doesn't change