Index: llvm/include/llvm/IR/Instructions.h
===================================================================
--- llvm/include/llvm/IR/Instructions.h
+++ llvm/include/llvm/IR/Instructions.h
@@ -2267,7 +2267,8 @@
                                      int &Index);
   static bool isExtractSubvectorMask(const Constant *Mask, int NumSrcElts,
                                      int &Index) {
-    assert(Mask->getType()->isVectorTy() && "Shuffle needs vector constant.");
+    assert(isa<FixedVectorType>(Mask->getType()) &&
+           "Shuffle needs vector constant.");
     SmallVector<int, 16> MaskAsInts;
     getShuffleMask(Mask, MaskAsInts);
     return isExtractSubvectorMask(MaskAsInts, NumSrcElts, Index);
@@ -2275,6 +2276,11 @@
 
   /// Return true if this shuffle mask is an extract subvector mask.
   bool isExtractSubvectorMask(int &Index) const {
+    // Not possible to express a shuffle mask for a scalable vector for this
+    // case.
+    if (isa<ScalableVectorType>(getType()))
+      return false;
+
     int NumSrcElts =
         cast<FixedVectorType>(Op<0>()->getType())->getNumElements();
     return isExtractSubvectorMask(ShuffleMask, NumSrcElts, Index);
Index: llvm/unittests/IR/InstructionsTest.cpp
===================================================================
--- llvm/unittests/IR/InstructionsTest.cpp
+++ llvm/unittests/IR/InstructionsTest.cpp
@@ -1073,6 +1073,17 @@
   EXPECT_FALSE(Id12->isIdentityWithExtract());
   EXPECT_FALSE(Id12->isConcat());
   delete Id12;
+
+  // Not possible to express shuffle mask for scalable vector for extract
+  // subvector.
+  Type *VScaleV4Int32Ty = ScalableVectorType::get(Int32Ty, 4);
+  ShuffleVectorInst *Id13 =
+      new ShuffleVectorInst(Constant::getAllOnesValue(VScaleV4Int32Ty),
+                            UndefValue::get(VScaleV4Int32Ty),
+                            Constant::getNullValue(VScaleV4Int32Ty));
+  int Index = 0;
+  EXPECT_FALSE(Id13->isExtractSubvectorMask(Index));
+  delete Id13;
 }
 
 TEST(InstructionsTest, GetSplat) {