diff --git a/src/backend/cpu/scan_by_key.cpp b/src/backend/cpu/scan_by_key.cpp
index d00db6c..f176840 100644
--- a/src/backend/cpu/scan_by_key.cpp
+++ b/src/backend/cpu/scan_by_key.cpp
@@ -31,6 +31,7 @@ namespace cpu
         kernel::scan_dim_by_key<op, Ti, Tk, To, 4> func4(inclusive_scan);

         in.eval();
+        key.eval();
         switch (in.ndims()) {
         case 1:
             getQueue().enqueue(func1, out, 0, key, 0, in, 0, dim);