diff --git a/mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorPasses.cpp b/mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorPasses.cpp
--- a/mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorPasses.cpp
+++ b/mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorPasses.cpp
@@ -166,6 +166,19 @@
     auto *ctx = &getContext();
     RewritePatternSet patterns(ctx);
     SparseTensorTypeToBufferConverter converter;
+    // Required by scf.for 1:N type conversion.
+    converter.addSourceMaterialization(
+        [](OpBuilder &builder, RankedTensorType tp, ValueRange inputs,
+           Location loc) -> Optional<Value> {
+          if (!getSparseTensorEncoding(tp))
+            // not a sparse tensor.
+            return llvm::None;
+          // Sparse compiler knows how to cancel out these casts.
+          return builder
+              .create<UnrealizedConversionCastOp>(loc, TypeRange(tp), inputs)
+              .getResult(0);
+        });
+
     ConversionTarget target(*ctx);
     // Most ops in the sparse dialect must go!
     target.addIllegalDialect<SparseTensorDialect>();