diff --git a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
--- a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
+++ b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
@@ -3104,11 +3104,15 @@
     IndexCastOpAdaptor transformed(operands);
 
     auto targetType =
-        typeConverter->convertType(indexCastOp.getResult().getType())
+        typeConverter->convertType(indexCastOp.getResult().getType());
+    auto targetElementType =
+        typeConverter
+            ->convertType(getElementTypeOrSelf(indexCastOp.getResult()))
             .cast<IntegerType>();
-    auto sourceType = transformed.in().getType().cast<IntegerType>();
-    unsigned targetBits = targetType.getWidth();
-    unsigned sourceBits = sourceType.getWidth();
+    auto sourceElementType =
+        getElementTypeOrSelf(transformed.in()).cast<IntegerType>();
+    unsigned targetBits = targetElementType.getWidth();
+    unsigned sourceBits = sourceElementType.getWidth();
 
     if (targetBits == sourceBits)
       rewriter.replaceOp(indexCastOp, transformed.in());
diff --git a/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir b/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir
--- a/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir
+++ b/mlir/test/Conversion/StandardToLLVM/convert-to-llvmir.mlir
@@ -520,6 +520,15 @@
   return
 }
 
+// CHECK-LABEL: @vector_index_cast
+func @vector_index_cast(%arg0: vector<2xindex>, %arg1: vector<2xi1>) {
+// CHECK-NEXT: = llvm.trunc %{{.*}} : vector<2xi{{.*}}> to vector<2xi1>
+  %0 = index_cast %arg0: vector<2xindex> to vector<2xi1>
+// CHECK-NEXT: = llvm.sext %{{.*}} : vector<2xi1> to vector<2xi{{.*}}>
+  %1 = index_cast %arg1: vector<2xi1> to vector<2xindex>
+  return
+}
+
 // Checking conversion of signed integer types to floating point.
 // CHECK-LABEL: @sitofp
 func @sitofp(%arg0 : i32, %arg1 : i64) {