diff --git a/mlir/lib/Dialect/SCF/SCF.cpp b/mlir/lib/Dialect/SCF/SCF.cpp
--- a/mlir/lib/Dialect/SCF/SCF.cpp
+++ b/mlir/lib/Dialect/SCF/SCF.cpp
@@ -2180,6 +2180,16 @@
     if (!innerOp)
       return failure();
 
+    // Merging loops with attributes is not supported yet.
+    // We need to figure out how to properly merge those attributes without
+    // losing information.
+    auto isUnexpectedAttr = [](mlir::NamedAttribute attr) {
+      return attr.getName() != ParallelOp::getOperandSegmentSizeAttr();
+    };
+    if (llvm::any_of(op->getAttrs(), isUnexpectedAttr) ||
+        llvm::any_of(innerOp->getAttrs(), isUnexpectedAttr))
+      return failure();
+
     auto hasVal = [](const auto &range, Value val) {
       return llvm::find(range, val) != range.end();
     };
diff --git a/mlir/test/Dialect/SCF/canonicalize.mlir b/mlir/test/Dialect/SCF/canonicalize.mlir
--- a/mlir/test/Dialect/SCF/canonicalize.mlir
+++ b/mlir/test/Dialect/SCF/canonicalize.mlir
@@ -134,6 +134,36 @@
 
 // -----
 
+func.func @nested_parallel_attr(%0: memref<?x?xf64>) -> memref<?x?xf64> {
+  %c0 = arith.constant 0 : index
+  %c1 = arith.constant 1 : index
+  %1 = memref.dim %0, %c0 : memref<?x?xf64>
+  %2 = memref.dim %0, %c1 : memref<?x?xf64>
+  %3 = memref.alloc(%1, %2) : memref<?x?xf64>
+  scf.parallel (%arg1) = (%c0) to (%1) step (%c1) {
+    scf.parallel (%arg2) = (%c0) to (%2) step (%c1) {
+      %4 = memref.load %0[%arg1, %arg2] : memref<?x?xf64>
+      memref.store %4, %3[%arg1, %arg2] : memref<?x?xf64>
+      scf.yield
+    } {mapping = [{bound = affine_map<(d0) -> (d0)>, map = affine_map<(d0) -> (d0)>, processor = 3 : i64}]}
+    scf.yield
+  } {mapping = [{bound = affine_map<(d0) -> (d0)>, map = affine_map<(d0) -> (d0)>, processor = 0 : i64}]}
+  return %3 : memref<?x?xf64>
+}
+
+// CHECK-LABEL:   func @nested_parallel_attr(
+// CHECK-DAG:       [[C0:%.*]] = arith.constant 0 : index
+// CHECK-DAG:       [[C1:%.*]] = arith.constant 1 : index
+// CHECK-DAG:       [[B0:%.*]] = memref.dim {{.*}}, [[C0]]
+// CHECK-DAG:       [[B1:%.*]] = memref.dim {{.*}}, [[C1]]
+// CHECK:           scf.parallel ([[V0:%.*]]) = ([[C0]]) to ([[B0]]) step ([[C1]])
+// CHECK:           scf.parallel ([[V1:%.*]]) = ([[C0]]) to ([[B1]]) step ([[C1]])
+// CHECK:           memref.load {{.*}}{{\[}}[[V0]], [[V1]]]
+// CHECK:           memref.store {{.*}}{{\[}}[[V0]], [[V1]]]
+// CHECK:           {mapping = {{.*}} processor = 3
+// CHECK:           {mapping = {{.*}} processor = 0
+// -----
+
 func.func private @side_effect()
 func.func @one_unused(%cond: i1) -> (index) {
   %0, %1 = scf.if %cond -> (index, index) {