diff --git a/flang/lib/Optimizer/Dialect/FIROps.cpp b/flang/lib/Optimizer/Dialect/FIROps.cpp
index 0543a624034ca..978120963c514 100644
--- a/flang/lib/Optimizer/Dialect/FIROps.cpp
+++ b/flang/lib/Optimizer/Dialect/FIROps.cpp
@@ -560,6 +560,16 @@ struct SimplifyArrayCoorOp : public mlir::OpRewritePattern<fir::ArrayCoorOp> {
         return mlir::failure();
     } else if (auto reboxOp = mlir::dyn_cast_or_null<fir::ReboxOp>(
                    memref.getDefiningOp())) {
+      // Don't pull in rebox when the array_coor is inside an ACC construct
+      // and the rebox result is referenced by an ACC data clause.
+      // The data legalization pipeline relies on the rebox result being the
+      // copyin var; folding through it would leave the rebox source as an
+      // unhandled live-in inside the compute region.
+      if (op->getParentOfType<ACC_COMPUTE_AND_DATA_CONSTRUCT_OPS>() &&
+          llvm::any_of(memref.getUsers(), [](mlir::Operation *u) {
+            return mlir::isa<ACC_DATA_ENTRY_OPS>(u);
+          }))
+        return mlir::failure();
       boxedMemref = reboxOp.getBox();
       boxedShape = reboxOp.getShape();
       // Avoid pulling in rebox that performs reshaping.
diff --git a/flang/test/Fir/array-coor-canonicalization-acc.fir b/flang/test/Fir/array-coor-canonicalization-acc.fir
new file mode 100644
index 0000000000000..5f6b8310a5ab9
--- /dev/null
+++ b/flang/test/Fir/array-coor-canonicalization-acc.fir
@@ -0,0 +1,48 @@
+// RUN: fir-opt --canonicalize --split-input-file %s | FileCheck %s
+
+// Verify that fir.rebox is NOT folded into fir.array_coor when the rebox
+// result is used by an acc.copyin. The data legalization pipeline depends on
+// the copyin's var (the rebox result) matching the value used inside compute
+// regions; folding would break this chain and produce an illegal live-in.
+// CHECK-LABEL:   func.func @test_acc_copyin_preserves_rebox(
+// CHECK-SAME:        %[[BOX:.*]]: !fir.box<!fir.array<?xf32>>,
+// CHECK-SAME:        %[[VAL:.*]]: f32) -> !fir.ref<f32> {
+// CHECK:           %[[C1:.*]] = arith.constant 1 : index
+// CHECK:           %[[REBOX:.*]] = fir.rebox %[[BOX]]
+// CHECK:           %[[COPYIN:.*]] = acc.copyin var(%[[REBOX]]
+// CHECK:           acc.parallel dataOperands(%[[COPYIN]] :
+// CHECK:             %[[COOR:.*]] = fir.array_coor %[[REBOX]] %[[C1]]
+// CHECK:             fir.store %[[VAL]] to %[[COOR]]
+// CHECK:             acc.yield
+// CHECK:           }
+// CHECK:           acc.copyout accVar(%[[COPYIN]]
+// CHECK:           %[[COOR_OUT:.*]] = fir.array_coor %[[BOX]] %[[C1]]
+// CHECK:           return %[[COOR_OUT]] : !fir.ref<f32>
+func.func @test_acc_copyin_preserves_rebox(%arg0: !fir.box<!fir.array<?xf32>>, %arg1: f32) -> !fir.ref<f32> {
+  %c1 = arith.constant 1 : index
+  %0 = fir.rebox %arg0 : (!fir.box<!fir.array<?xf32>>) -> !fir.box<!fir.array<?xf32>>
+  %1 = acc.copyin var(%0 : !fir.box<!fir.array<?xf32>>) -> !fir.box<!fir.array<?xf32>> {dataClause = #acc<data_clause acc_copy>, name = "array"}
+  acc.parallel dataOperands(%1 : !fir.box<!fir.array<?xf32>>) {
+    %2 = fir.array_coor %0 %c1 : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+    fir.store %arg1 to %2 : !fir.ref<f32>
+    acc.yield
+  } attributes {defaultAttr = #acc<defaultvalue none>}
+  acc.copyout accPtr(%1 : !fir.box<!fir.array<?xf32>>) to varPtr(%0 : !fir.box<!fir.array<?xf32>>) {dataClause = #acc<data_clause acc_copy>, name = "array"}
+  %3 = fir.array_coor %0 %c1 : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+  return %3 : !fir.ref<f32>
+}
+
+// -----
+
+// Same scenario but without acc.copyin: rebox SHOULD be folded normally.
+// CHECK-LABEL:   func.func @test_no_acc_folds_rebox(
+// CHECK-SAME:        %[[BOX:.*]]: !fir.box<!fir.array<?xf32>>) -> !fir.ref<f32> {
+// CHECK:           %[[C1:.*]] = arith.constant 1 : index
+// CHECK:           %[[COOR:.*]] = fir.array_coor %[[BOX]] %[[C1]]
+// CHECK:           return %[[COOR]] : !fir.ref<f32>
+func.func @test_no_acc_folds_rebox(%arg0: !fir.box<!fir.array<?xf32>>) -> !fir.ref<f32> {
+  %c1 = arith.constant 1 : index
+  %0 = fir.rebox %arg0 : (!fir.box<!fir.array<?xf32>>) -> !fir.box<!fir.array<?xf32>>
+  %2 = fir.array_coor %0 %c1 : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+  return %2 : !fir.ref<f32>
+}