diff --git a/renderdoc/driver/shaders/spirv/spirv_debug_glsl450.cpp b/renderdoc/driver/shaders/spirv/spirv_debug_glsl450.cpp
index 44f14a967..b77a78aef 100644
--- a/renderdoc/driver/shaders/spirv/spirv_debug_glsl450.cpp
+++ b/renderdoc/driver/shaders/spirv/spirv_debug_glsl450.cpp
@@ -255,6 +255,43 @@ ShaderVariable MatrixInverse(ThreadState &state, uint32_t, const rdcarray<Id> &p
   return m;
 }
 
+ShaderVariable Modf(ThreadState &state, uint32_t, const rdcarray<Id> &params)
+{
+  CHECK_PARAMS(2);
+
+  ShaderVariable x = state.GetSrc(params[0]);
+  Id iptr = params[1];
+
+  ShaderVariable whole = x;
+
+  for(uint32_t c = 0; c < x.columns; c++)
+    x.value.fv[c] = modff(x.value.fv[c], &whole.value.fv[c]);
+
+  state.WritePointerValue(iptr, whole);
+
+  return x;
+}
+
+ShaderVariable ModfStruct(ThreadState &state, uint32_t, const rdcarray<Id> &params)
+{
+  CHECK_PARAMS(1);
+
+  ShaderVariable x = state.GetSrc(params[0]);
+
+  ShaderVariable ret;
+  ret.rows = 1;
+  ret.columns = 1;
+  ret.isStruct = true;
+  ret.members = {x, x};
+  ret.members[0].name = "_child0";
+  ret.members[1].name = "_child1";
+
+  for(uint32_t c = 0; c < x.columns; c++)
+    ret.members[0].value.fv[c] = modff(x.value.fv[c], &ret.members[1].value.fv[c]);
+
+  return ret;
+}
+
 template <typename T>
 static T GLSLMax(T x, T y)
 {
@@ -442,6 +479,43 @@ ShaderVariable SmoothStep(ThreadState &state, uint32_t, const rdcarray<Id> &para
   return x;
 }
 
+ShaderVariable Frexp(ThreadState &state, uint32_t, const rdcarray<Id> &params)
+{
+  CHECK_PARAMS(2);
+
+  ShaderVariable x = state.GetSrc(params[0]);
+  Id iptr = params[1];
+
+  ShaderVariable whole = x;
+
+  for(uint32_t c = 0; c < x.columns; c++)
+    x.value.fv[c] = frexpf(x.value.fv[c], &whole.value.iv[c]);
+
+  state.WritePointerValue(iptr, whole);
+
+  return x;
+}
+
+ShaderVariable FrexpStruct(ThreadState &state, uint32_t, const rdcarray<Id> &params)
+{
+  CHECK_PARAMS(1);
+
+  ShaderVariable x = state.GetSrc(params[0]);
+
+  ShaderVariable ret;
+  ret.rows = 1;
+  ret.columns = 1;
+  ret.isStruct = true;
+  ret.members = {x, x};
+  ret.members[0].name = "_child0";
+  ret.members[1].name = "_child1";
+
+  for(uint32_t c = 0; c < x.columns; c++)
+    ret.members[0].value.fv[c] = frexpf(x.value.fv[c], &ret.members[1].value.iv[c]);
+
+  return ret;
+}
+
 ShaderVariable Ldexp(ThreadState &state, uint32_t, const rdcarray<Id> &params)
 {
   CHECK_PARAMS(2);
@@ -617,6 +691,8 @@ void ConfigureGLSLStd450(ExtInstDispatcher &extinst)
   EXT(Degrees);
   EXT(Determinant);
   EXT(MatrixInverse);
+  EXT(Modf);
+  EXT(ModfStruct);
   EXT(FMin);
   EXT(UMin);
   EXT(SMin);
@@ -629,6 +705,8 @@ void ConfigureGLSLStd450(ExtInstDispatcher &extinst)
   EXT(FMix);
   EXT(Step);
   EXT(SmoothStep);
+  EXT(Frexp);
+  EXT(FrexpStruct);
   EXT(Ldexp);
   EXT(Cross);
   EXT(FaceForward);
diff --git a/util/test/demos/vk/vk_shader_debug_zoo.cpp b/util/test/demos/vk/vk_shader_debug_zoo.cpp
index c88e07ba3..ba6d02f01 100644
--- a/util/test/demos/vk/vk_shader_debug_zoo.cpp
+++ b/util/test/demos/vk/vk_shader_debug_zoo.cpp
@@ -1341,6 +1341,25 @@ void main()
         "%_out_float = OpExtInst %float %glsl450 NClamp %nan %zerof %oneVal",
     });
 
+    // test ExtInst Modf/ModfStruct and Frexp/FrexpStruct
+    append_tests({
+        "%_x = OpExtInst %float %glsl450 Modf %float_dyn_123_456 %priv_float\n"
+        "%_y = OpLoad %float %priv_float\n"
+        "%_tmp = OpExtInst %f32f32 %glsl450 ModfStruct %float_dyn_789_012\n"
+        "%_z = OpCompositeExtract %float %_tmp 0\n"
+        "%_w = OpCompositeExtract %float %_tmp 1\n"
+        "%_out_float4 = OpCompositeConstruct %float4 %_x %_y %_z %_w\n",
+
+        "%_x = OpExtInst %float %glsl450 Frexp %float_dyn_123_456 %priv_int\n"
+        "%_yi = OpLoad %int %priv_int\n"
+        "%_y = OpConvertSToF %float %_yi\n"
+        "%_tmp = OpExtInst %f32i32 %glsl450 FrexpStruct %float_dyn_789_012\n"
+        "%_z = OpCompositeExtract %float %_tmp 0\n"
+        "%_wi = OpCompositeExtract %int %_tmp 1\n"
+        "%_w = OpConvertSToF %float %_wi\n"
+        "%_out_float4 = OpCompositeConstruct %float4 %_x %_y %_z %_w\n",
+    });
+
     // test float <-> int conversions
     append_tests({
         "%_x = OpConvertUToF %float %uint_dyn_1234\n"
@@ -1645,6 +1664,9 @@ void main()
       %child = OpTypeStruct %float4 %float3 %float
      %parent = OpTypeStruct %float4 %child %float4x4
 
+     %f32f32 = OpTypeStruct %float %float
+     %f32i32 = OpTypeStruct %float %int
+
     %ptr_Input_v2f = OpTypePointer Input %v2f
 %ptr_Input_flatv2f = OpTypePointer Input %flatv2f
    %ptr_Input_uint = OpTypePointer Input %uint
@@ -1653,12 +1675,17 @@ void main()
  %ptr_Input_float2 = OpTypePointer Input %float2
  %ptr_Input_float4 = OpTypePointer Input %float4
 %ptr_Output_float4 = OpTypePointer Output %float4
+  %ptr_Private_int = OpTypePointer Private %int
+%ptr_Private_float = OpTypePointer Private %float
 
   %linearData = OpVariable %ptr_Input_v2f Input
     %flatData = OpVariable %ptr_Input_flatv2f Input
 %gl_FragCoord = OpVariable %ptr_Input_float4 Input
        %Color = OpVariable %ptr_Output_float4 Output
 
+    %priv_int = OpVariable %ptr_Private_int Private
+  %priv_float = OpVariable %ptr_Private_float Private
+
        %flatv2f_test_idx = OpConstant %int 0
      %flatv2f_intval_idx = OpConstant %int 1