diff --git a/renderdoc/driver/shaders/spirv/spirv_debug_setup.cpp b/renderdoc/driver/shaders/spirv/spirv_debug_setup.cpp
index 397e62ff4..9aa914723 100644
--- a/renderdoc/driver/shaders/spirv/spirv_debug_setup.cpp
+++ b/renderdoc/driver/shaders/spirv/spirv_debug_setup.cpp
@@ -543,6 +543,11 @@ ShaderDebugTrace *Debugger::BeginDebug(DebugAPIWrapper *apiWrapper, const Shader
 
           this->apiWrapper->FillInputValue(var, builtin, (uint32_t)location, component);
         }
+        else
+        {
+          // make it obvious when uninitialised outputs are written
+          memset(var.value.u64v, 0xcc, sizeof(var.value.u64v));
+        }
 
         if(sourceName != rawName)
         {
@@ -885,8 +890,19 @@ ShaderDebugTrace *Debugger::BeginDebug(DebugAPIWrapper *apiWrapper, const Shader
       // global variables should all be pointers into opaque storage
       RDCASSERT(type.type == DataType::PointerType);
 
+      auto uninitialisedCallback = [this](ShaderVariable &var, const Decorations &,
+                                          const DataType &, uint64_t, const rdcstr &) {
+        if(!var.members.empty())
+          return;
+
+        memset(var.value.u64v, 0xcc, sizeof(var.value.u64v));
+      };
+
       WalkVariable<ShaderVariable, true>(decorations[v.id], dataTypes[type.InnerType()], ~0U, var,
-                                         rdcstr(), NULL);
+                                         rdcstr(), uninitialisedCallback);
+
+      if(v.initializer != Id())
+        AssignValue(var, active.ids[v.initializer]);
 
       if(v.storage == StorageClass::Private)
       {
diff --git a/renderdoc/driver/shaders/spirv/spirv_processor.cpp b/renderdoc/driver/shaders/spirv/spirv_processor.cpp
index 1b2936be8..95f0f0266 100644
--- a/renderdoc/driver/shaders/spirv/spirv_processor.cpp
+++ b/renderdoc/driver/shaders/spirv/spirv_processor.cpp
@@ -492,7 +492,8 @@ void Processor::RegisterOp(Iter it)
 
     // only register global variables here
     if(decoded.storageClass != rdcspv::StorageClass::Function)
-      globals.push_back(Variable(decoded.resultType, decoded.result, decoded.storageClass));
+      globals.push_back(
+          Variable(decoded.resultType, decoded.result, decoded.storageClass, decoded.initializer));
   }
   else if(opdata.op == Op::ConstantNull)
   {
diff --git a/renderdoc/driver/shaders/spirv/spirv_processor.h b/renderdoc/driver/shaders/spirv/spirv_processor.h
index ce4aa7ca4..55c1293f9 100644
--- a/renderdoc/driver/shaders/spirv/spirv_processor.h
+++ b/renderdoc/driver/shaders/spirv/spirv_processor.h
@@ -430,10 +430,11 @@ struct EntryPoint
 struct Variable
 {
   Variable() = default;
-  Variable(Id t, Id i, StorageClass s) : type(t), id(i), storage(s) {}
+  Variable(Id t, Id i, StorageClass s, Id init) : type(t), id(i), storage(s), initializer(init) {}
   Id type;
   Id id;
   StorageClass storage;
+  Id initializer;
 
   bool operator<(const Variable &o) const
   {
@@ -441,13 +442,15 @@ struct Variable
       return id < o.id;
     if(type != o.type)
       return type < o.type;
-    return storage < o.storage;
+    if(storage != o.storage)
+      return storage < o.storage;
+    return initializer < o.initializer;
   }
 
   bool operator!=(const Variable &o) const { return !operator==(o); }
   bool operator==(const Variable &o) const
   {
-    return id == o.id && type == o.type && storage == o.storage;
+    return id == o.id && type == o.type && storage == o.storage && initializer == o.initializer;
   }
 };
 
diff --git a/util/test/demos/vk/vk_shader_debug_zoo.cpp b/util/test/demos/vk/vk_shader_debug_zoo.cpp
index 3e23e3988..ef5532e27 100644
--- a/util/test/demos/vk/vk_shader_debug_zoo.cpp
+++ b/util/test/demos/vk/vk_shader_debug_zoo.cpp
@@ -2438,6 +2438,30 @@ void main()
         %_mat = OpLoad %float4x4 %_ptrmat
 
  %_out_float4 = OpMatrixTimesVector %float4 %_mat %_vec
+)EOTEST",
+    });
+
+    // test variables with initialisers
+    append_tests({
+        R"EOTEST(
+                 ; this has a constant initialiser, so should already be ready
+ %_out_float4 = OpLoad %float4 %priv_float4_init
+)EOTEST",
+        R"EOTEST(
+                 ; this is uninitialised, but unforuntately that means we can't test our debugging
+                 ; against the real thing when it's undefined. But we can at least expose it so that
+                 ; when manually checking we see the uninitialised values
+     %_uninit = OpLoad %float4 %priv_float4
+          %_x = OpVectorTimesScalar %float4 %_uninit %float_0_0
+ %_out_float4 = OpFAdd %float4 %_x %float4_1234
+)EOTEST",
+        R"EOTEST(
+                 ; this is uninitialised, but unforuntately that means we can't test our debugging
+                 ; against the real thing when it's undefined. But we can at least expose it so that
+                 ; when manually checking we see the uninitialised values
+     %_uninit = OpLoad %float4 %Color
+          %_x = OpVectorTimesScalar %float4 %_uninit %float_0_0
+ %_out_float4 = OpFAdd %float4 %_x %float4_1234
 )EOTEST",
     });
   }
@@ -2916,6 +2940,8 @@ OpMemberDecorate %cbuffer_struct 17 Offset 216    ; double doublePackSource
  %float2_00 = OpConstantComposite %float2 %float_0_0 %float_0_0
  %float2_12 = OpConstantComposite %float2 %float_1_0 %float_2_0
 
+  %priv_float4_init = OpVariable %ptr_Private_float4 Private %float4_1234
+
 )EOSHADER";
 
     std::string ret = capabilities +