diff --git a/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp b/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
--- a/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
+++ b/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
@@ -1140,7 +1140,8 @@
   /// deletion.
   void finalizeLowering(Instruction *Inst, MatrixTy Matrix,
                         IRBuilder<> &Builder) {
-    Inst2ColumnMatrix.insert(std::make_pair(Inst, Matrix));
+    auto inserted = Inst2ColumnMatrix.insert(std::make_pair(Inst, Matrix));
+    assert(inserted.second && "multiple matrix lowering mapping");
 
     ToRemove.push_back(Inst);
     Value *Flattened = nullptr;
@@ -1540,11 +1541,11 @@
       if (Transpose->hasOneUse()) {
         FusedInsts.insert(cast<Instruction>(Transpose));
         ToRemove.push_back(cast<Instruction>(Transpose));
+        // TODO: add a fake entry for the folded instruction so that this is
+        // included in the expression in the remark.
+        Inst2ColumnMatrix[Transpose] = MatrixTy(M, C, EltType);
       }
       finalizeLowering(MatMul, Result, Builder);
-      // TODO: add a fake entry for the folded instruction so that this is
-      // included in the expression in the remark.
-      Inst2ColumnMatrix[Transpose] = MatrixTy(M, C, EltType);
       return;
     }
 
diff --git a/llvm/test/Transforms/LowerMatrixIntrinsics/multiply-right-transpose.ll b/llvm/test/Transforms/LowerMatrixIntrinsics/multiply-right-transpose.ll
--- a/llvm/test/Transforms/LowerMatrixIntrinsics/multiply-right-transpose.ll
+++ b/llvm/test/Transforms/LowerMatrixIntrinsics/multiply-right-transpose.ll
@@ -91,10 +91,10 @@
 ; CHECK-NEXT:    [[TMP11:%.*]] = insertelement <3 x double> [[TMP9]], double [[TMP10]], i64 2
 ; CHECK-NEXT:    [[TMP12:%.*]] = bitcast <6 x double>* [[P:%.*]] to double*
 ; CHECK-NEXT:    [[VEC_CAST:%.*]] = bitcast double* [[TMP12]] to <3 x double>*
-; CHECK-NEXT:    store <3 x double> undef, <3 x double>* [[VEC_CAST]], align 16
+; CHECK-NEXT:    store <3 x double> [[TMP5]], <3 x double>* [[VEC_CAST]], align 16
 ; CHECK-NEXT:    [[VEC_GEP:%.*]] = getelementptr double, double* [[TMP12]], i64 3
 ; CHECK-NEXT:    [[VEC_CAST42:%.*]] = bitcast double* [[VEC_GEP]] to <3 x double>*
-; CHECK-NEXT:    store <3 x double> undef, <3 x double>* [[VEC_CAST42]], align 8
+; CHECK-NEXT:    store <3 x double> [[TMP11]], <3 x double>* [[VEC_CAST42]], align 8
 ; CHECK-NEXT:    [[SPLIT:%.*]] = shufflevector <6 x double> [[A:%.*]], <6 x double> poison, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:    [[SPLIT1:%.*]] = shufflevector <6 x double> [[A]], <6 x double> poison, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:    [[SPLIT2:%.*]] = shufflevector <6 x double> [[A]], <6 x double> poison, <2 x i32> <i32 4, i32 5>