diff --git a/lib/HLSL/HLOperationLower.cpp b/lib/HLSL/HLOperationLower.cpp
index c9c9bb4c88..b0ba051875 100644
--- a/lib/HLSL/HLOperationLower.cpp
+++ b/lib/HLSL/HLOperationLower.cpp
@@ -8189,7 +8189,7 @@ void TranslateCBAddressUserLegacy(Instruction *user, Value *handle,
           // row.z = c[2].[idx]
           // row.w = c[3].[idx]
           Value *Elts[4];
-          ArrayType *AT = ArrayType::get(EltTy, MatTy.getNumColumns());
+          ArrayType *AT = ArrayType::get(EltTy, MatTy.getNumRows());
 
           IRBuilder<> AllocaBuilder(user->getParent()
                                         ->getParent()
diff --git a/tools/clang/test/DXC/Passes/DxilGen/cb-col-matrix-subscript-dxilgen.ll b/tools/clang/test/DXC/Passes/DxilGen/cb-col-matrix-subscript-dxilgen.ll
new file mode 100644
index 0000000000..14d8d93b1f
--- /dev/null
+++ b/tools/clang/test/DXC/Passes/DxilGen/cb-col-matrix-subscript-dxilgen.ll
@@ -0,0 +1,158 @@
+; RUN: %dxopt %s -hlsl-passes-resume -dxilgen -S | FileCheck %s
+
+; Source HLSL:
+; // dxc -T cs_6_0
+; float3x2 M;
+; RWStructuredBuffer<float2> SB;
+; [numthreads(3,1,1)]
+; void main(uint row : SV_GroupIndex) {
+;     SB[row] = M[row];
+; }
+
+; Check cbuffer column-major matrix subscript codegen uses correct alloca size.
+
+; Column-major matrix subscript is lowered in HLOperationLower by:
+; Loading one column into an alloca, dynamically indexing that by row,
+; then doing the same for the next column.
+; Each column is 3 floats for 3 rows. Thus alloca size should be 3 floats.
+
+; alloca size should be number of rows (3), not number of columns (2)
+; CHECK: %[[alloca:[^ ]+]] = alloca [3 x float]
+; CHECK: %[[row:[^ ]+]] = call i32 @dx.op.flattenedThreadIdInGroup.i32(i32 96)
+; CHECK: %[[cb0:[^ ]+]] = call %dx.types.CBufRet.f32 @dx.op.cbufferLoadLegacy.f32(i32 59, %dx.types.Handle %[[cbh:[^ ]+]], i32 0)
+; CHECK: %[[_cb_ex0:[^ ]+]] = extractvalue %dx.types.CBufRet.f32 %[[cb0]], 0
+; CHECK: %[[_v3x:[^ ]+]] = insertelement <3 x float> undef, float %[[_cb_ex0]], i64 0
+; CHECK: %[[_cb_ex1:[^ ]+]] = extractvalue %dx.types.CBufRet.f32 %[[cb0]], 1
+; CHECK: %[[_v3xy:[^ ]+]] = insertelement <3 x float> %[[_v3x]], float %[[_cb_ex1]], i64 1
+; CHECK: %[[_cb_ex2:[^ ]+]] = extractvalue %dx.types.CBufRet.f32 %[[cb0]], 2
+; CHECK: %[[_v3xyz:[^ ]+]] = insertelement <3 x float> %[[_v3xy]], float %[[_cb_ex2]], i64 2
+; CHECK: %[[cb0_x:[^ ]+]] = extractelement <3 x float> %[[_v3xyz]], i32 0
+; CHECK: %[[_alloca_0:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 0
+; CHECK: store float %[[cb0_x]], float* %[[_alloca_0]]
+; CHECK: %[[cb0_y:[^ ]+]] = extractelement <3 x float> %[[_v3xyz]], i32 1
+; CHECK: %[[_alloca_1:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 1
+; CHECK: store float %[[cb0_y]], float* %[[_alloca_1]]
+; CHECK: %[[cb0_z:[^ ]+]] = extractelement <3 x float> %[[_v3xyz]], i32 2
+; CHECK: %[[_alloca_2:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 2
+; CHECK: store float %[[cb0_z]], float* %[[_alloca_2]]
+; CHECK: %[[_alloca_row:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 %[[row]]
+; CHECK: %[[M_row_0:[^ ]+]] = load float, float* %[[_alloca_row]]
+; CHECK: %[[cb1:[^ ]+]] = call %dx.types.CBufRet.f32 @dx.op.cbufferLoadLegacy.f32(i32 59, %dx.types.Handle %[[cbh]], i32 1)
+; CHECK: %[[_cb_ex0:[^ ]+]] = extractvalue %dx.types.CBufRet.f32 %[[cb1]], 0
+; CHECK: %[[_v3x:[^ ]+]] = insertelement <3 x float> undef, float %[[_cb_ex0]], i64 0
+; CHECK: %[[_cb_ex1:[^ ]+]] = extractvalue %dx.types.CBufRet.f32 %[[cb1]], 1
+; CHECK: %[[_v3xy:[^ ]+]] = insertelement <3 x float> %[[_v3x]], float %[[_cb_ex1]], i64 1
+; CHECK: %[[_cb_ex2:[^ ]+]] = extractvalue %dx.types.CBufRet.f32 %[[cb1]], 2
+; CHECK: %[[_v3xyz:[^ ]+]] = insertelement <3 x float> %[[_v3xy]], float %[[_cb_ex2]], i64 2
+; CHECK: %[[cb1_x:[^ ]+]] = extractelement <3 x float> %[[_v3xyz]], i32 0
+; CHECK: %[[_alloca_0:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 0
+; CHECK: store float %[[cb1_x]], float* %[[_alloca_0]]
+; CHECK: %[[cb1_y:[^ ]+]] = extractelement <3 x float> %[[_v3xyz]], i32 1
+; CHECK: %[[_alloca_1:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 1
+; CHECK: store float %[[cb1_y]], float* %[[_alloca_1]]
+; CHECK: %[[cb1_z:[^ ]+]] = extractelement <3 x float> %[[_v3xyz]], i32 2
+; CHECK: %[[_alloca_2:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 2
+; CHECK: store float %[[cb1_z]], float* %[[_alloca_2]]
+; CHECK: %[[_alloca_row:[^ ]+]] = getelementptr inbounds [3 x float], [3 x float]* %[[alloca]], i32 0, i32 %[[row]]
+; CHECK: %[[M_row_1:[^ ]+]] = load float, float* %[[_alloca_row]]
+; CHECK: %[[M_row_v2x:[^ ]+]] = insertelement <2 x float> undef, float %[[M_row_0]], i64 0
+; CHECK: %[[M_row_v2xy:[^ ]+]] = insertelement <2 x float> %[[M_row_v2x]], float %[[M_row_1]], i64 1
+; CHECK: %[[ex_M_row_0:[^ ]+]] = extractelement <2 x float> %[[M_row_v2xy]], i64 0
+; CHECK: %[[ex_M_row_1:[^ ]+]] = extractelement <2 x float> %[[M_row_v2xy]], i64 1
+; CHECK: call void @dx.op.rawBufferStore.f32(i32 140, %dx.types.Handle %{{[^,]+}}, i32 %[[row]], i32 0, float %[[ex_M_row_0]], float %[[ex_M_row_1]], float undef, float undef, i8 3, i32 4)
+
+target datalayout = "e-m:e-p:32:32-i1:32-i8:32-i16:32-i32:32-i64:64-f16:32-f32:32-f64:64-n8:16:32:64"
+target triple = "dxil-ms-dx"
+
+%"class.RWStructuredBuffer<vector<float, 2> >" = type { <2 x float> }
+%"$Globals" = type { %class.matrix.float.3.2 }
+%class.matrix.float.3.2 = type { [3 x <2 x float>] }
+%dx.types.Handle = type { i8* }
+%dx.types.ResourceProperties = type { i32, i32 }
+
+@"\01?SB@@3V?$RWStructuredBuffer@V?$vector@M$01@@@@A" = external global %"class.RWStructuredBuffer<vector<float, 2> >", align 4
+@"$Globals" = external constant %"$Globals"
+
+; Function Attrs: nounwind
+define void @main(i32 %row) #0 {
+entry:
+  %0 = call %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %\22$Globals\22*, i32)"(i32 0, %"$Globals"* @"$Globals", i32 0)
+  %1 = call %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %\22$Globals\22)"(i32 14, %dx.types.Handle %0, %dx.types.ResourceProperties { i32 13, i32 28 }, %"$Globals" undef)
+  %2 = call %"$Globals"* @"dx.hl.subscript.cb.rn.%\22$Globals\22* (i32, %dx.types.Handle, i32)"(i32 6, %dx.types.Handle %1, i32 0)
+  %3 = getelementptr inbounds %"$Globals", %"$Globals"* %2, i32 0, i32 0
+  %4 = add i32 3, %row
+  %5 = call <2 x float>* @"dx.hl.subscript.colMajor[].rn.<2 x float>* (i32, %class.matrix.float.3.2*, i32, i32)"(i32 1, %class.matrix.float.3.2* %3, i32 %row, i32 %4)
+  %6 = load <2 x float>, <2 x float>* %5
+  %7 = load %"class.RWStructuredBuffer<vector<float, 2> >", %"class.RWStructuredBuffer<vector<float, 2> >"* @"\01?SB@@3V?$RWStructuredBuffer@V?$vector@M$01@@@@A"
+  %8 = call %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %\22class.RWStructuredBuffer<vector<float, 2> >\22)"(i32 0, %"class.RWStructuredBuffer<vector<float, 2> >" %7)
+  %9 = call %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %\22class.RWStructuredBuffer<vector<float, 2> >\22)"(i32 14, %dx.types.Handle %8, %dx.types.ResourceProperties { i32 4108, i32 8 }, %"class.RWStructuredBuffer<vector<float, 2> >" zeroinitializer)
+  %10 = call <2 x float>* @"dx.hl.subscript.[].rn.<2 x float>* (i32, %dx.types.Handle, i32)"(i32 0, %dx.types.Handle %9, i32 %row)
+  store <2 x float> %6, <2 x float>* %10
+  ret void
+}
+
+; Function Attrs: nounwind readnone
+declare <2 x float>* @"dx.hl.subscript.colMajor[].rn.<2 x float>* (i32, %class.matrix.float.3.2*, i32, i32)"(i32, %class.matrix.float.3.2*, i32, i32) #1
+
+; Function Attrs: nounwind readnone
+declare <2 x float>* @"dx.hl.subscript.[].rn.<2 x float>* (i32, %dx.types.Handle, i32)"(i32, %dx.types.Handle, i32) #1
+
+; Function Attrs: nounwind readnone
+declare %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %\22class.RWStructuredBuffer<vector<float, 2> >\22)"(i32, %"class.RWStructuredBuffer<vector<float, 2> >") #1
+
+; Function Attrs: nounwind readnone
+declare %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %\22class.RWStructuredBuffer<vector<float, 2> >\22)"(i32, %dx.types.Handle, %dx.types.ResourceProperties, %"class.RWStructuredBuffer<vector<float, 2> >") #1
+
+; Function Attrs: nounwind readnone
+declare %"$Globals"* @"dx.hl.subscript.cb.rn.%\22$Globals\22* (i32, %dx.types.Handle, i32)"(i32, %dx.types.Handle, i32) #1
+
+; Function Attrs: nounwind readnone
+declare %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %\22$Globals\22*, i32)"(i32, %"$Globals"*, i32) #1
+
+; Function Attrs: nounwind readnone
+declare %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %\22$Globals\22)"(i32, %dx.types.Handle, %dx.types.ResourceProperties, %"$Globals") #1
+
+attributes #0 = { nounwind }
+attributes #1 = { nounwind readnone }
+
+!pauseresume = !{!0}
+!llvm.ident = !{!1}
+!dx.fnprops = !{!2}
+!dx.options = !{!3, !4}
+!dx.version = !{!5}
+!dx.valver = !{!6}
+!dx.shaderModel = !{!7}
+!dx.resources = !{!8}
+!dx.typeAnnotations = !{!14, !20}
+!dx.entryPoints = !{!27}
+
+!0 = !{!"hlsl-hlemit", !"hlsl-hlensure"}
+!1 = !{!"dxc(private) 1.8.0.15080 (main, c52246122)"}
+!2 = !{void (i32)* @main, i32 5, i32 3, i32 1, i32 1}
+!3 = !{i32 -2147483584}
+!4 = !{i32 -1}
+!5 = !{i32 1, i32 0}
+!6 = !{i32 1, i32 10}
+!7 = !{!"cs", i32 6, i32 0}
+!8 = !{null, !9, !12, null}
+!9 = !{!10}
+!10 = !{i32 0, %"class.RWStructuredBuffer<vector<float, 2> >"* @"\01?SB@@3V?$RWStructuredBuffer@V?$vector@M$01@@@@A", !"SB", i32 -1, i32 -1, i32 1, i32 12, i1 false, i1 false, i1 false, !11}
+!11 = !{i32 1, i32 8}
+!12 = !{!13}
+!13 = !{i32 0, %"$Globals"* @"$Globals", !"$Globals", i32 0, i32 -1, i32 1, i32 28, null}
+!14 = !{i32 0, %"class.RWStructuredBuffer<vector<float, 2> >" undef, !15, %"$Globals" undef, !17}
+!15 = !{i32 8, !16}
+!16 = !{i32 6, !"h", i32 3, i32 0, i32 7, i32 9}
+!17 = !{i32 28, !18}
+!18 = !{i32 6, !"M", i32 2, !19, i32 3, i32 0, i32 7, i32 9}
+!19 = !{i32 3, i32 2, i32 2}
+!20 = !{i32 1, void (i32)* @main, !21}
+!21 = !{!22, !24}
+!22 = !{i32 1, !23, !23}
+!23 = !{}
+!24 = !{i32 0, !25, !26}
+!25 = !{i32 4, !"SV_GroupIndex", i32 7, i32 5}
+!26 = !{i32 0}
+!27 = !{void (i32)* @main, !"main", null, !8, !28}
+!28 = !{i32 4, !29}
+!29 = !{i32 -858993460, i32 -858993460, i32 -858993460}